chart (geography)

1 Presentation

chart (geography), representation drawn or printed on a surface punt of a geographical area generally corresponding to a portion of the surface of the Earth.In the majority of the cases, a chart is a diagrammatic representation rather than illustrated of a given zone;it contains usually various commonly allowed symbols, which indicate the inherent characteristics, artificial or cultural of the area represented.

The essential problems involved in the development of a chart are the representation of a curved surface (Earth or part of the Earth) on a plan, and the choice of the scale.Before the appearance of the computers (see Cartography), the establishment of charts required multiple talents:capacity to discover and select information coming from various sources on various aspects of the geography, then to synthesize the results in a whole of data simple, coherent and exact;gifts of originator to create the final chart able to correctly communicate the "message" intended for readers of various origins;a manual dexterity to represent information by using symbols, lines and colors to make readable the whole of the chart;knowledge of graphic design to simplify often complex reasons.

There is not a "correct" way to make a chart.The way in which it is carried out depends on the goal of the chart, the tools available to the cartographer and its knowledge.

Chart of the world of the xve century

2 Types of chart

One can use charts for various reasons, which explains the existence of various types of specialized charts.

2.1 Topographic charts

The topographic charts are generally used to represent terrestrial areas.They indicate the inherent and artificial characteristics of the area represented:they can thus comprise the grid system (roads, railways, channels, paths, airports), hydrography (river, lakes, aspects of the coasts), the dwellings (villages, boroughs, cities), the form and the altitude of the relief, etc.The political limits, which mark separations between departments, areas and States are also specified.Because of the great diversity of information which they comprise, the topographic charts are generally used as charts of reference for an everyday usage.

2.2 Specialized charts

The sea charts and aeronautical are among most significant of the specialized charts.The sea charts are used for navigation;they cover the oceans.Figures indicating the depth of water to low tide are laid out with intervals brought closer on the corresponding parts of the chart.The shallow waters and the hollows are surrounded by a circle or in are grayed so that they appear more clearly, and the limits of the channels are indicated by lines.The nature of the bottom (sand, mud, rock, etc.)is also specified.The exact localization of the headlights, the buoys and other assistances with navigation is one of the significant characteristics of the sea charts.Certain reference marks of the coasts, like raised buildings or peaks, are also indicated because they make it possible to the navigator to establish his position.The aeronautical charts that one uses in flight resemble the topographic charts somewhat;they indicate in more the site of the radio beacons, the air routes and the zones covered by the channels of radio guidance.

Among other charts specialized appear charts political, which retains topographic characteristics only the limits of the cities and the borders political, geological maps, which shows the geological structure of a zone, like good of other charts, which indicate for example the geographical distribution of harvests, the use of the ground, the height of precipitations, the number of inhabitants.The relief maps represent an area given in three dimensions.To accentuate the relief, the vertical scale represents several times the horizontal scale in general.The relief maps are very much used for the design of plans in engineering and in the military field.

Chart of Eastern Europe

Est

3 fundamental Characteristics of a chart

The recourse to a system of symbols is essential to easily read a significant quantity of information.Many symbols frequently used in general are well accepted and are immediately included/understood.Thus the cities, large and small, are indicated by points or zones of shade;the rivers and the rivers are often printed in blue, just as the stretches of water;the political borders are marked by ribbons of color or dotted lines.A cartographer can however be brought to create a great number of symbols to satisfy such or such need.For example, a tent can indicate the presence of a camp-site and cross pickaxes can mark the site of a mine.The legend of the chart explains the symbols used.

3.1 Geographical grid

It is necessary to refer to the geographical grid of the chart to locate a point or to indicate the extent of a zone.This grid is consisted by the meridian lines in longitude and the parallels in latitude.To convention, one counts 180 of longitude is and 180 of western longitude compared to the meridian line of Greenwich, which has as a value 0.In the same way, one counts 90 of northern latitude and 90 of southern latitude compared to the parallel of the equator, which has as a value 0.Each point on a chart can be defined with precision by indicating its value in degrees, minutes and seconds for the latitude and longitude.True north is in general placed in top of the chart, which also contains a pink of the winds directed towards the magnetic pole or another indication of a magnetic variation.

3.2 Scale

The scale represents the existing relationship between the distance which separates two points on the Earth and its representation on the chart.The scale is in general appeared as figures, like 1/100 000, which means that unit measured on the chart (in fact 1 cm) corresponds to 100 000 times the same unit on the surface of the Earth.The scale is specified in the margin of the majority of the charts, which often also present a tick-marked line indicating the length on the scale of one, of five or ten units, often of the kilometers.

The charts on a very large scale (higher than 1/10 000) are called plane.The large-scale maps go from 1/10 000 (where 1 cm on paper is equivalent to 100 m on the ground) to 1/25 000, the average scale goes up to 1/100 000 and the small scale starts with the charts with 1/200 000 (where 1 cm on paper is equivalent to 2 km on the ground) or 1/250 000.

The most detailed large-scale maps are often those which show the property of the grounds and the buildings.These charts are often made on scales varying between 1/500 and 1/5 000 and it is not need to generalize or simplify much the information which one wants to represent.The more one zone is densément populated, the more the scale used will be large.

The charts on a small scale, as those which are reproduced on the atlases, must on the other hand be strongly simplified.The roads, for example, are often widened and can be moved to facilitate perception, provided that they remain placed correctly the ones compared to the others.

The ordinary topographic charts, as those which are produced by the national geographical Institute (IGN), are on a 1/100 000 scale, 1/50 000 and 1/25 000.For the military charts, the scale can go up to 1/15 800.Since the beginning of the century, a certain number of countries take part in the development of a standard chart of the world on a 1/1 000 000 scale.

3.3 Representation of the relief

The relief is represented by level lines, which join the points of the zone concerned which are with the same altitude.The value of the interval between each curve can vary, because it depends on the importance of the relief and the scale of the chart;for example, interval can to be of 50 m, so that the cartographer, when it draws the chart, connects by a feature initially all the points which are to 50 m above the sea level, then those which are to 100 m, 150 m and so on.The shape of the level lines gives an exact idea of the shape of the hills and depressions, of which the heights and the depths are indicated by the curves themselves.Thus, the strong slopes are revealed by brought closer curves.

It is possible also to indicate the heights by using various colors or dyed, as well as hatchings (short parallel lines) or shades.In the case of the colors, one represents the of the same zones height while exploiting various colours;for example, all the part ranging between 0 and 100 m above the sea level is colored in clear green, the part between 100 and 200 m appears in a darker colour and so on.The hatchings are used to indicate the slopes;they are all the more marked and brought closer that the slope is accentuated.In fact often only the slopes exposed to south-east are hatched or ombrées, which suggests to some extent a sight of plane of the area lit by the light of the North-West.The carefully drawn shades and hatchings do not indicate the heights, but they are more easily interpreted than the level lines, and one uses them sometimes together for reasons of clearness.
4 Projections

To post this section with the printable format

A chart must have the shape of a sphere to represent all the surface of the Earth without introducing deformation;one speaks in this case about sphere.A chart punt cannot appear with precision a round surface, apart from not very wide areas where the curve of the Earth is negligible.

When it is a question of representing areas of average or large size accurately, the chart must propose a compromise between deformations relating to surface, the distance and the direction.In certain cases, the cartographer can privilege one of these elements to the detriment of the others, which lose then in precision.One employs the term of projections to indicate the various ways of preparing a chart with two dimensions of the surface of the Earth;one distinguishes geometrical projections from analytical projections, according to the technique of development adopted.Geometrical projections are classified according to the type of surface used for the establishment of the chart, like the cylinders, the cones or the plans;plane projections are also indicated by the term of azimuth or zenith projections.Analytical projections are based on mathematical calculations.

4.1 Cylindrical projections

When it carries out a cylindrical projection, the cartographer considers the surface of the chart as a cylinder which surrounds the sphere and is in contact with this one on the level of the equator.The parallels are prolonged apart from the sphere, as parallel plans which cut the cylinder, while remaining parallel to the equator.Because of the sphericity of the sphere, the parallels near the poles are gradually brought closer from/to each other when they are projected on the cylinder;moreover, the projected meridian lines are represented like parallel straight lines, which are perpendicular to the equator and are prolonged towards the North Poles and South.Once projection carried out, the cylinder is supposed to be cut out in the vertical direction then unrolled flat.

The chart obtained represents the surface of the world like a rectangle with in longitude the regularly spaced meridian lines and latitude the parallels laid out in an unequal way.Although the areas are very deformed near the poles on a cylindrical projection, one finds on the chart the proportions which are those of the areas in reality.

The Flemish geographer Gerardus Mercator was based on mathematics to develop a well-known type of projection which bears its name and are connected, with certain modifications, with cylindrical projection.A chart of Mercator is precise for the equatorial areas, but appreciably deforms the areas located in high latitudes.However, the directions are represented accurately, which is particularly interesting for navigation and corresponded to the preliminary draft of Mercator.Any line cutting two meridian lines or more according to the same angle is represented on a chart of Mercator by a straight line, called line of rhumb.This one represents in the case of a ship or a plane a direct road established using a compass.A navigator can decide his road using a chart of Mercator by simply tracing a line between two points and while following on the chart the direction given by the compass.
4.2
Azimuth projection

Azimuth projection corresponds to a projection of the sphere on a plane surface which can be in contact with the sphere at any point.Azimuth projections gather plane projections of type gnomonic, orthographical and stereographic.The azimuth projection of surface equalizes and equidistant azimuth projection return to two other types of plane projections;they cannot be projected, but are conceived according to a tangent plan (in contact).Gnomonic projection corresponds to projected rays of the center of the Earth.In an orthographical projection, the source of the rays is ad infinitum, and the charts designed according to this process give the impression that the Earth was photographed since cosmos.In the case of a stereographic projection, the source of the rays is a point which is diametrically opposed to the tangent of the plan on which projection is carried out.

The nature of projection varies according to the source of the rays.Thus, gnomonic projection covers zones smaller than a hemisphere whereas orthographical projection covers the hemispheres;equivalent azimuth projection and stereographic projection correspond to broader zones, and equidistant azimuth projection relates to the entire sphere.However, in all these types of projection (except for equidistant projection azimuth), the part of the Earth which appears on the chart depends on the point on contact on the imaginary plan with the Earth.A chart of projection planes whose plan is tangent on the surface of the Earth on the level of the equator represents the zone of the equator, but cannot be reproduced all the area on a chart;if the plan is tangent with the one of the poles, the chart represents the polar areas.

Insofar as the source of gnomonic projection is in the center of the Earth, all the large circles (the equator, each meridian line and all other circles dividing the sphere into two equal parts) are represented like straight lines.A large circle which connects two points on the Earth always corresponds to the shortest distance between these two points.This is why the gnomonic chart is very useful for navigation when it is used with the chart of Mercator.

4.3 conical projections

In this type of projection, one supposes that a cone is placed at the top of the sphere.After projection, the cone is supposed being cut out and unrolled on a plane surface.The cone is in contact with the sphere on each point of only one parallel;the chart obtained is extremely precise for all the zones located close to the parallel, but it becomes very deformed for all the other zones, by respecting the exact report/ratio of the distance from these zones to the standard parallel.

To reach a highher degree of accuracy, the conical projection in conformity of Lambert starts from a cone which passes by part of surface of the sphere and cut two parallels.Because of the precision obtained by this type of chart in the immediate proximity of the two parallels, the zone represented between the standard parallels is deformed than the same zone reproduced by a single conical projection.

Polyconic projection is a type of projection much more complex, which brings into play a series of cones, each one of them being in contact with the sphere with a parallel different, and only the zone in the vicinity immediate of each parallel is used.By gathering the results of the series of limited conical projections, it is possible to cover a broad zone with a very high degree of accuracy.Because a cone cannot be in contact with the sphere in the polar and equatorial areas most distant, various conical projections are used to represent relatively small areas in the moderate zones.The polyconic charts offer a good compromise between the representation of surface, the distance and the direction in the case of small areas.

4.4 Mathematical calculation

A certain number of projections, according to the devoted term, were developed using mathematics to appear in detail of the significant zones in a small scale.The charts based on mathematical calculations represent the whole Earth in circles, ovals or according to other forms'.In the case of specialized charts, the Earth is often drawn while not following the original form of projection, but with joined and irregular parts.The charts of this type are called stopped projections and include/understand the projection of Goode and the equivalent projection of Eckert.

5
Realization of a chart
To post this section with the printable format

The most significant progress in the manufacture of the charts came from the techniques of remote collecting, i.e. techniques which truly gather data on an object without the touch, in particular the air photography (which includes/understands photography with infra-red) and photographs it by satellite.Total Positioning System (GPS) implements the triangulation by satellite, which reduced the margin of error considerably when it is a question of locating exactly points on the surface of the Earth.The recourse to the computer to draw charts counts among the most recent innovations

5.1
Observation

A chart rests essentially on a meticulous survey of the geographical sites and relations existing between a great number of points in the area considered.Today, almost all the original charts call upon the aerial observation in addition to the information obtained by the usual techniques of topography.The images obtained by satellite get a great number of precise information concerning the site of mineral deposits, the tentacular urban development, the penetration of the vegetation and the various types of grounds.

5.2 Compilation and reproduction

Once the data gathered, the chart must carefully be prepared according to its final destination so that all relevant information is communicated clearly and precision.The surveys and the photographs carried out are then used to enter a great number of points on a grid of cross lines which correspond to the projection chosen for the chart.The heights are indicated and the level lines, if they are used, are directly drawn from stereoscopic pairs of photographs.The roads, the rivers and the rivers are drawn according to the same process, as well as the site of the other elements of the chart.

The preparation of a chart for the impression starts with a series of sheets, at a rate of a sheet for each color used.These sheets are composed of a plastic covered with an opaque substance;the lines and the symbols are traced on surface using a sharp-edged instrument of engraving which removes the opaque layer, according to a technique which concerns the lithography.Each one of these sheets constitutes negative from which is carried out a lithographic plate.

There are also orthophotocartes, whose base is made up true photographs.The charts of this type are a mosaic of parts of carefully cut out air photographs, which were modified using a orthophotoscope to eliminate the deformations from scale and angle.It is possible to record information on the co-ordinates of a geographical area and on the distribution of the statistical phenomena of this zone.An instrument as a continuous graph plotter makes it possible a computer to carry out charts by using the recorded data.It is possible to post on a video screen the charts created by computer, which can be easily modified by an operator.The charts of this kind make it possible to provide an animated image of a change for one determined period, because the data of the chart and the later modifications are recorded.

chart (geography)

1 Presentation

chart (geography), representation drawn or printed on a surface punt of a geographical area generally corresponding to a portion of the surface of the Earth.In the majority of the cases, a chart is a diagrammatic representation rather than illustrated of a given zone;it contains usually various commonly allowed symbols, which indicate the inherent characteristics, artificial or cultural of the area represented.

The essential problems involved in the development of a chart are the representation of a curved surface (Earth or part of the Earth) on a plan, and the choice of the scale.Before the appearance of the computers (see Cartography), the establishment of charts required multiple talents:capacity to discover and select information coming from various sources on various aspects of the geography, then to synthesize the results in a whole of data simple, coherent and exact;gifts of originator to create the final chart able to correctly communicate the "message" intended for readers of various origins;a manual dexterity to represent information by using symbols, lines and colors to make readable the whole of the chart;knowledge of graphic design to simplify often complex reasons.

There is not a "correct" way to make a chart.The way in which it is carried out depends on the goal of the chart, the tools available to the cartographer and its knowledge.

Chart of the world of the xve century

2 Types of chart

One can use charts for various reasons, which explains the existence of various types of specialized charts.

2.1 Topographic charts

The topographic charts are generally used to represent terrestrial areas.They indicate the inherent and artificial characteristics of the area represented:they can thus comprise the grid system (roads, railways, channels, paths, airports), hydrography (river, lakes, aspects of the coasts), the dwellings (villages, boroughs, cities), the form and the altitude of the relief, etc.The political limits, which mark separations between departments, areas and States are also specified.Because of the great diversity of information which they comprise, the topographic charts are generally used as charts of reference for an everyday usage.

2.2 Specialized charts

The sea charts and aeronautical are among most significant of the specialized charts.The sea charts are used for navigation;they cover the oceans.Figures indicating the depth of water to low tide are laid out with intervals brought closer on the corresponding parts of the chart.The shallow waters and the hollows are surrounded by a circle or in are grayed so that they appear more clearly, and the limits of the channels are indicated by lines.The nature of the bottom (sand, mud, rock, etc.)is also specified.The exact localization of the headlights, the buoys and other assistances with navigation is one of the significant characteristics of the sea charts.Certain reference marks of the coasts, like raised buildings or peaks, are also indicated because they make it possible to the navigator to establish his position.The aeronautical charts that one uses in flight resemble the topographic charts somewhat;they indicate in more the site of the radio beacons, the air routes and the zones covered by the channels of radio guidance.

Among other charts specialized appear charts political, which retains topographic characteristics only the limits of the cities and the borders political, geological maps, which shows the geological structure of a zone, like good of other charts, which indicate for example the geographical distribution of harvests, the use of the ground, the height of precipitations, the number of inhabitants.The relief maps represent an area given in three dimensions.To accentuate the relief, the vertical scale represents several times the horizontal scale in general.The relief maps are very much used for the design of plans in engineering and in the military field.

Chart of Eastern Europe

Est

3 fundamental Characteristics of a chart

The recourse to a system of symbols is essential to easily read a significant quantity of information.Many symbols frequently used in general are well accepted and are immediately included/understood.Thus the cities, large and small, are indicated by points or zones of shade;the rivers and the rivers are often printed in blue, just as the stretches of water;the political borders are marked by ribbons of color or dotted lines.A cartographer can however be brought to create a great number of symbols to satisfy such or such need.For example, a tent can indicate the presence of a camp-site and cross pickaxes can mark the site of a mine.The legend of the chart explains the symbols used.

3.1 Geographical grid

It is necessary to refer to the geographical grid of the chart to locate a point or to indicate the extent of a zone.This grid is consisted by the meridian lines in longitude and the parallels in latitude.To convention, one counts 180 of longitude is and 180 of western longitude compared to the meridian line of Greenwich, which has as a value 0.In the same way, one counts 90 of northern latitude and 90 of southern latitude compared to the parallel of the equator, which has as a value 0.Each point on a chart can be defined with precision by indicating its value in degrees, minutes and seconds for the latitude and longitude.True north is in general placed in top of the chart, which also contains a pink of the winds directed towards the magnetic pole or another indication of a magnetic variation.

3.2 Scale

The scale represents the existing relationship between the distance which separates two points on the Earth and its representation on the chart.The scale is in general appeared as figures, like 1/100 000, which means that unit measured on the chart (in fact 1 cm) corresponds to 100 000 times the same unit on the surface of the Earth.The scale is specified in the margin of the majority of the charts, which often also present a tick-marked line indicating the length on the scale of one, of five or ten units, often of the kilometers.

The charts on a very large scale (higher than 1/10 000) are called plane.The large-scale maps go from 1/10 000 (where 1 cm on paper is equivalent to 100 m on the ground) to 1/25 000, the average scale goes up to 1/100 000 and the small scale starts with the charts with 1/200 000 (where 1 cm on paper is equivalent to 2 km on the ground) or 1/250 000.

The most detailed large-scale maps are often those which show the property of the grounds and the buildings.These charts are often made on scales varying between 1/500 and 1/5 000 and it is not need to generalize or simplify much the information which one wants to represent.The more one zone is densément populated, the more the scale used will be large.

The charts on a small scale, as those which are reproduced on the atlases, must on the other hand be strongly simplified.The roads, for example, are often widened and can be moved to facilitate perception, provided that they remain placed correctly the ones compared to the others.

The ordinary topographic charts, as those which are produced by the national geographical Institute (IGN), are on a 1/100 000 scale, 1/50 000 and 1/25 000.For the military charts, the scale can go up to 1/15 800.Since the beginning of the century, a certain number of countries take part in the development of a standard chart of the world on a 1/1 000 000 scale.

3.3 Representation of the relief

The relief is represented by level lines, which join the points of the zone concerned which are with the same altitude.The value of the interval between each curve can vary, because it depends on the importance of the relief and the scale of the chart;for example, interval can to be of 50 m, so that the cartographer, when it draws the chart, connects by a feature initially all the points which are to 50 m above the sea level, then those which are to 100 m, 150 m and so on.The shape of the level lines gives an exact idea of the shape of the hills and depressions, of which the heights and the depths are indicated by the curves themselves.Thus, the strong slopes are revealed by brought closer curves.

It is possible also to indicate the heights by using various colors or dyed, as well as hatchings (short parallel lines) or shades.In the case of the colors, one represents the of the same zones height while exploiting various colours;for example, all the part ranging between 0 and 100 m above the sea level is colored in clear green, the part between 100 and 200 m appears in a darker colour and so on.The hatchings are used to indicate the slopes;they are all the more marked and brought closer that the slope is accentuated.In fact often only the slopes exposed to south-east are hatched or ombrées, which suggests to some extent a sight of plane of the area lit by the light of the North-West.The carefully drawn shades and hatchings do not indicate the heights, but they are more easily interpreted than the level lines, and one uses them sometimes together for reasons of clearness.
4 Projections

To post this section with the printable format

A chart must have the shape of a sphere to represent all the surface of the Earth without introducing deformation;one speaks in this case about sphere.A chart punt cannot appear with precision a round surface, apart from not very wide areas where the curve of the Earth is negligible.

When it is a question of representing areas of average or large size accurately, the chart must propose a compromise between deformations relating to surface, the distance and the direction.In certain cases, the cartographer can privilege one of these elements to the detriment of the others, which lose then in precision.One employs the term of projections to indicate the various ways of preparing a chart with two dimensions of the surface of the Earth;one distinguishes geometrical projections from analytical projections, according to the technique of development adopted.Geometrical projections are classified according to the type of surface used for the establishment of the chart, like the cylinders, the cones or the plans;plane projections are also indicated by the term of azimuth or zenith projections.Analytical projections are based on mathematical calculations.

4.1 Cylindrical projections

When it carries out a cylindrical projection, the cartographer considers the surface of the chart as a cylinder which surrounds the sphere and is in contact with this one on the level of the equator.The parallels are prolonged apart from the sphere, as parallel plans which cut the cylinder, while remaining parallel to the equator.Because of the sphericity of the sphere, the parallels near the poles are gradually brought closer from/to each other when they are projected on the cylinder;moreover, the projected meridian lines are represented like parallel straight lines, which are perpendicular to the equator and are prolonged towards the North Poles and South.Once projection carried out, the cylinder is supposed to be cut out in the vertical direction then unrolled flat.

The chart obtained represents the surface of the world like a rectangle with in longitude the regularly spaced meridian lines and latitude the parallels laid out in an unequal way.Although the areas are very deformed near the poles on a cylindrical projection, one finds on the chart the proportions which are those of the areas in reality.

The Flemish geographer Gerardus Mercator was based on mathematics to develop a well-known type of projection which bears its name and are connected, with certain modifications, with cylindrical projection.A chart of Mercator is precise for the equatorial areas, but appreciably deforms the areas located in high latitudes.However, the directions are represented accurately, which is particularly interesting for navigation and corresponded to the preliminary draft of Mercator.Any line cutting two meridian lines or more according to the same angle is represented on a chart of Mercator by a straight line, called line of rhumb.This one represents in the case of a ship or a plane a direct road established using a compass.A navigator can decide his road using a chart of Mercator by simply tracing a line between two points and while following on the chart the direction given by the compass.
4.2
Azimuth projection

Azimuth projection corresponds to a projection of the sphere on a plane surface which can be in contact with the sphere at any point.Azimuth projections gather plane projections of type gnomonic, orthographical and stereographic.The azimuth projection of surface equalizes and equidistant azimuth projection return to two other types of plane projections;they cannot be projected, but are conceived according to a tangent plan (in contact).Gnomonic projection corresponds to projected rays of the center of the Earth.In an orthographical projection, the source of the rays is ad infinitum, and the charts designed according to this process give the impression that the Earth was photographed since cosmos.In the case of a stereographic projection, the source of the rays is a point which is diametrically opposed to the tangent of the plan on which projection is carried out.

The nature of projection varies according to the source of the rays.Thus, gnomonic projection covers zones smaller than a hemisphere whereas orthographical projection covers the hemispheres;equivalent azimuth projection and stereographic projection correspond to broader zones, and equidistant azimuth projection relates to the entire sphere.However, in all these types of projection (except for equidistant projection azimuth), the part of the Earth which appears on the chart depends on the point on contact on the imaginary plan with the Earth.A chart of projection planes whose plan is tangent on the surface of the Earth on the level of the equator represents the zone of the equator, but cannot be reproduced all the area on a chart;if the plan is tangent with the one of the poles, the chart represents the polar areas.

Insofar as the source of gnomonic projection is in the center of the Earth, all the large circles (the equator, each meridian line and all other circles dividing the sphere into two equal parts) are represented like straight lines.A large circle which connects two points on the Earth always corresponds to the shortest distance between these two points.This is why the gnomonic chart is very useful for navigation when it is used with the chart of Mercator.

4.3 conical projections

In this type of projection, one supposes that a cone is placed at the top of the sphere.After projection, the cone is supposed being cut out and unrolled on a plane surface.The cone is in contact with the sphere on each point of only one parallel;the chart obtained is extremely precise for all the zones located close to the parallel, but it becomes very deformed for all the other zones, by respecting the exact report/ratio of the distance from these zones to the standard parallel.

To reach a highher degree of accuracy, the conical projection in conformity of Lambert starts from a cone which passes by part of surface of the sphere and cut two parallels.Because of the precision obtained by this type of chart in the immediate proximity of the two parallels, the zone represented between the standard parallels is deformed than the same zone reproduced by a single conical projection.

Polyconic projection is a type of projection much more complex, which brings into play a series of cones, each one of them being in contact with the sphere with a parallel different, and only the zone in the vicinity immediate of each parallel is used.By gathering the results of the series of limited conical projections, it is possible to cover a broad zone with a very high degree of accuracy.Because a cone cannot be in contact with the sphere in the polar and equatorial areas most distant, various conical projections are used to represent relatively small areas in the moderate zones.The polyconic charts offer a good compromise between the representation of surface, the distance and the direction in the case of small areas.

4.4 Mathematical calculation

A certain number of projections, according to the devoted term, were developed using mathematics to appear in detail of the significant zones in a small scale.The charts based on mathematical calculations represent the whole Earth in circles, ovals or according to other forms'.In the case of specialized charts, the Earth is often drawn while not following the original form of projection, but with joined and irregular parts.The charts of this type are called stopped projections and include/understand the projection of Goode and the equivalent projection of Eckert.

5
Realization of a chart
To post this section with the printable format

The most significant progress in the manufacture of the charts came from the techniques of remote collecting, i.e. techniques which truly gather data on an object without the touch, in particular the air photography (which includes/understands photography with infra-red) and photographs it by satellite.Total Positioning System (GPS) implements the triangulation by satellite, which reduced the margin of error considerably when it is a question of locating exactly points on the surface of the Earth.The recourse to the computer to draw charts counts among the most recent innovations

5.1
Observation

A chart rests essentially on a meticulous survey of the geographical sites and relations existing between a great number of points in the area considered.Today, almost all the original charts call upon the aerial observation in addition to the information obtained by the usual techniques of topography.The images obtained by satellite get a great number of precise information concerning the site of mineral deposits, the tentacular urban development, the penetration of the vegetation and the various types of grounds.

5.2 Compilation and reproduction

Once the data gathered, the chart must carefully be prepared according to its final destination so that all relevant information is communicated clearly and precision.The surveys and the photographs carried out are then used to enter a great number of points on a grid of cross lines which correspond to the projection chosen for the chart.The heights are indicated and the level lines, if they are used, are directly drawn from stereoscopic pairs of photographs.The roads, the rivers and the rivers are drawn according to the same process, as well as the site of the other elements of the chart.

The preparation of a chart for the impression starts with a series of sheets, at a rate of a sheet for each color used.These sheets are composed of a plastic covered with an opaque substance;the lines and the symbols are traced on surface using a sharp-edged instrument of engraving which removes the opaque layer, according to a technique which concerns the lithography.Each one of these sheets constitutes negative from which is carried out a lithographic plate.

There are also orthophotocartes, whose base is made up true photographs.The charts of this type are a mosaic of parts of carefully cut out air photographs, which were modified using a orthophotoscope to eliminate the deformations from scale and angle.It is possible to record information on the co-ordinates of a geographical area and on the distribution of the statistical phenomena of this zone.An instrument as a continuous graph plotter makes it possible a computer to carry out charts by using the recorded data.It is possible to post on a video screen the charts created by computer, which can be easily modified by an operator.The charts of this kind make it possible to provide an animated image of a change for one determined period, because the data of the chart and the later modifications are recorded.

chart (geography)

1 Presentation

chart (geography), representation drawn or printed on a surface punt of a geographical area generally corresponding to a portion of the surface of the Earth.In the majority of the cases, a chart is a diagrammatic representation rather than illustrated of a given zone;it contains usually various commonly allowed symbols, which indicate the inherent characteristics, artificial or cultural of the area represented.

The essential problems involved in the development of a chart are the representation of a curved surface (Earth or part of the Earth) on a plan, and the choice of the scale.Before the appearance of the computers (see Cartography), the establishment of charts required multiple talents:capacity to discover and select information coming from various sources on various aspects of the geography, then to synthesize the results in a whole of data simple, coherent and exact;gifts of originator to create the final chart able to correctly communicate the "message" intended for readers of various origins;a manual dexterity to represent information by using symbols, lines and colors to make readable the whole of the chart;knowledge of graphic design to simplify often complex reasons.

There is not a "correct" way to make a chart.The way in which it is carried out depends on the goal of the chart, the tools available to the cartographer and its knowledge.

Chart of the world of the xve century

2 Types of chart

One can use charts for various reasons, which explains the existence of various types of specialized charts.

2.1 Topographic charts

The topographic charts are generally used to represent terrestrial areas.They indicate the inherent and artificial characteristics of the area represented:they can thus comprise the grid system (roads, railways, channels, paths, airports), hydrography (river, lakes, aspects of the coasts), the dwellings (villages, boroughs, cities), the form and the altitude of the relief, etc.The political limits, which mark separations between departments, areas and States are also specified.Because of the great diversity of information which they comprise, the topographic charts are generally used as charts of reference for an everyday usage.

2.2 Specialized charts

The sea charts and aeronautical are among most significant of the specialized charts.The sea charts are used for navigation;they cover the oceans.Figures indicating the depth of water to low tide are laid out with intervals brought closer on the corresponding parts of the chart.The shallow waters and the hollows are surrounded by a circle or in are grayed so that they appear more clearly, and the limits of the channels are indicated by lines.The nature of the bottom (sand, mud, rock, etc.)is also specified.The exact localization of the headlights, the buoys and other assistances with navigation is one of the significant characteristics of the sea charts.Certain reference marks of the coasts, like raised buildings or peaks, are also indicated because they make it possible to the navigator to establish his position.The aeronautical charts that one uses in flight resemble the topographic charts somewhat;they indicate in more the site of the radio beacons, the air routes and the zones covered by the channels of radio guidance.

Among other charts specialized appear charts political, which retains topographic characteristics only the limits of the cities and the borders political, geological maps, which shows the geological structure of a zone, like good of other charts, which indicate for example the geographical distribution of harvests, the use of the ground, the height of precipitations, the number of inhabitants.The relief maps represent an area given in three dimensions.To accentuate the relief, the vertical scale represents several times the horizontal scale in general.The relief maps are very much used for the design of plans in engineering and in the military field.

Chart of Eastern Europe

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3 fundamental Characteristics of a chart

The recourse to a system of symbols is essential to easily read a significant quantity of information.Many symbols frequently used in general are well accepted and are immediately included/understood.Thus the cities, large and small, are indicated by points or zones of shade;the rivers and the rivers are often printed in blue, just as the stretches of water;the political borders are marked by ribbons of color or dotted lines.A cartographer can however be brought to create a great number of symbols to satisfy such or such need.For example, a tent can indicate the presence of a camp-site and cross pickaxes can mark the site of a mine.The legend of the chart explains the symbols used.

3.1 Geographical grid

It is necessary to refer to the geographical grid of the chart to locate a point or to indicate the extent of a zone.This grid is consisted by the meridian lines in longitude and the parallels in latitude.To convention, one counts 180 of longitude is and 180 of western longitude compared to the meridian line of Greenwich, which has as a value 0.In the same way, one counts 90 of northern latitude and 90 of southern latitude compared to the parallel of the equator, which has as a value 0.Each point on a chart can be defined with precision by indicating its value in degrees, minutes and seconds for the latitude and longitude.True north is in general placed in top of the chart, which also contains a pink of the winds directed towards the magnetic pole or another indication of a magnetic variation.

3.2 Scale

The scale represents the existing relationship between the distance which separates two points on the Earth and its representation on the chart.The scale is in general appeared as figures, like 1/100 000, which means that unit measured on the chart (in fact 1 cm) corresponds to 100 000 times the same unit on the surface of the Earth.The scale is specified in the margin of the majority of the charts, which often also present a tick-marked line indicating the length on the scale of one, of five or ten units, often of the kilometers.

The charts on a very large scale (higher than 1/10 000) are called plane.The large-scale maps go from 1/10 000 (where 1 cm on paper is equivalent to 100 m on the ground) to 1/25 000, the average scale goes up to 1/100 000 and the small scale starts with the charts with 1/200 000 (where 1 cm on paper is equivalent to 2 km on the ground) or 1/250 000.

The most detailed large-scale maps are often those which show the property of the grounds and the buildings.These charts are often made on scales varying between 1/500 and 1/5 000 and it is not need to generalize or simplify much the information which one wants to represent.The more one zone is densément populated, the more the scale used will be large.

The charts on a small scale, as those which are reproduced on the atlases, must on the other hand be strongly simplified.The roads, for example, are often widened and can be moved to facilitate perception, provided that they remain placed correctly the ones compared to the others.

The ordinary topographic charts, as those which are produced by the national geographical Institute (IGN), are on a 1/100 000 scale, 1/50 000 and 1/25 000.For the military charts, the scale can go up to 1/15 800.Since the beginning of the century, a certain number of countries take part in the development of a standard chart of the world on a 1/1 000 000 scale.

3.3 Representation of the relief

The relief is represented by level lines, which join the points of the zone concerned which are with the same altitude.The value of the interval between each curve can vary, because it depends on the importance of the relief and the scale of the chart;for example, interval can to be of 50 m, so that the cartographer, when it draws the chart, connects by a feature initially all the points which are to 50 m above the sea level, then those which are to 100 m, 150 m and so on.The shape of the level lines gives an exact idea of the shape of the hills and depressions, of which the heights and the depths are indicated by the curves themselves.Thus, the strong slopes are revealed by brought closer curves.

It is possible also to indicate the heights by using various colors or dyed, as well as hatchings (short parallel lines) or shades.In the case of the colors, one represents the of the same zones height while exploiting various colours;for example, all the part ranging between 0 and 100 m above the sea level is colored in clear green, the part between 100 and 200 m appears in a darker colour and so on.The hatchings are used to indicate the slopes;they are all the more marked and brought closer that the slope is accentuated.In fact often only the slopes exposed to south-east are hatched or ombrées, which suggests to some extent a sight of plane of the area lit by the light of the North-West.The carefully drawn shades and hatchings do not indicate the heights, but they are more easily interpreted than the level lines, and one uses them sometimes together for reasons of clearness.
4 Projections

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A chart must have the shape of a sphere to represent all the surface of the Earth without introducing deformation;one speaks in this case about sphere.A chart punt cannot appear with precision a round surface, apart from not very wide areas where the curve of the Earth is negligible.

When it is a question of representing areas of average or large size accurately, the chart must propose a compromise between deformations relating to surface, the distance and the direction.In certain cases, the cartographer can privilege one of these elements to the detriment of the others, which lose then in precision.One employs the term of projections to indicate the various ways of preparing a chart with two dimensions of the surface of the Earth;one distinguishes geometrical projections from analytical projections, according to the technique of development adopted.Geometrical projections are classified according to the type of surface used for the establishment of the chart, like the cylinders, the cones or the plans;plane projections are also indicated by the term of azimuth or zenith projections.Analytical projections are based on mathematical calculations.

4.1 Cylindrical projections

When it carries out a cylindrical projection, the cartographer considers the surface of the chart as a cylinder which surrounds the sphere and is in contact with this one on the level of the equator.The parallels are prolonged apart from the sphere, as parallel plans which cut the cylinder, while remaining parallel to the equator.Because of the sphericity of the sphere, the parallels near the poles are gradually brought closer from/to each other when they are projected on the cylinder;moreover, the projected meridian lines are represented like parallel straight lines, which are perpendicular to the equator and are prolonged towards the North Poles and South.Once projection carried out, the cylinder is supposed to be cut out in the vertical direction then unrolled flat.

The chart obtained represents the surface of the world like a rectangle with in longitude the regularly spaced meridian lines and latitude the parallels laid out in an unequal way.Although the areas are very deformed near the poles on a cylindrical projection, one finds on the chart the proportions which are those of the areas in reality.

The Flemish geographer Gerardus Mercator was based on mathematics to develop a well-known type of projection which bears its name and are connected, with certain modifications, with cylindrical projection.A chart of Mercator is precise for the equatorial areas, but appreciably deforms the areas located in high latitudes.However, the directions are represented accurately, which is particularly interesting for navigation and corresponded to the preliminary draft of Mercator.Any line cutting two meridian lines or more according to the same angle is represented on a chart of Mercator by a straight line, called line of rhumb.This one represents in the case of a ship or a plane a direct road established using a compass.A navigator can decide his road using a chart of Mercator by simply tracing a line between two points and while following on the chart the direction given by the compass.
4.2
Azimuth projection

Azimuth projection corresponds to a projection of the sphere on a plane surface which can be in contact with the sphere at any point.Azimuth projections gather plane projections of type gnomonic, orthographical and stereographic.The azimuth projection of surface equalizes and equidistant azimuth projection return to two other types of plane projections;they cannot be projected, but are conceived according to a tangent plan (in contact).Gnomonic projection corresponds to projected rays of the center of the Earth.In an orthographical projection, the source of the rays is ad infinitum, and the charts designed according to this process give the impression that the Earth was photographed since cosmos.In the case of a stereographic projection, the source of the rays is a point which is diametrically opposed to the tangent of the plan on which projection is carried out.

The nature of projection varies according to the source of the rays.Thus, gnomonic projection covers zones smaller than a hemisphere whereas orthographical projection covers the hemispheres;equivalent azimuth projection and stereographic projection correspond to broader zones, and equidistant azimuth projection relates to the entire sphere.However, in all these types of projection (except for equidistant projection azimuth), the part of the Earth which appears on the chart depends on the point on contact on the imaginary plan with the Earth.A chart of projection planes whose plan is tangent on the surface of the Earth on the level of the equator represents the zone of the equator, but cannot be reproduced all the area on a chart;if the plan is tangent with the one of the poles, the chart represents the polar areas.

Insofar as the source of gnomonic projection is in the center of the Earth, all the large circles (the equator, each meridian line and all other circles dividing the sphere into two equal parts) are represented like straight lines.A large circle which connects two points on the Earth always corresponds to the shortest distance between these two points.This is why the gnomonic chart is very useful for navigation when it is used with the chart of Mercator.

4.3 conical projections

In this type of projection, one supposes that a cone is placed at the top of the sphere.After projection, the cone is supposed being cut out and unrolled on a plane surface.The cone is in contact with the sphere on each point of only one parallel;the chart obtained is extremely precise for all the zones located close to the parallel, but it becomes very deformed for all the other zones, by respecting the exact report/ratio of the distance from these zones to the standard parallel.

To reach a highher degree of accuracy, the conical projection in conformity of Lambert starts from a cone which passes by part of surface of the sphere and cut two parallels.Because of the precision obtained by this type of chart in the immediate proximity of the two parallels, the zone represented between the standard parallels is deformed than the same zone reproduced by a single conical projection.

Polyconic projection is a type of projection much more complex, which brings into play a series of cones, each one of them being in contact with the sphere with a parallel different, and only the zone in the vicinity immediate of each parallel is used.By gathering the results of the series of limited conical projections, it is possible to cover a broad zone with a very high degree of accuracy.Because a cone cannot be in contact with the sphere in the polar and equatorial areas most distant, various conical projections are used to represent relatively small areas in the moderate zones.The polyconic charts offer a good compromise between the representation of surface, the distance and the direction in the case of small areas.

4.4 Mathematical calculation

A certain number of projections, according to the devoted term, were developed using mathematics to appear in detail of the significant zones in a small scale.The charts based on mathematical calculations represent the whole Earth in circles, ovals or according to other forms'.In the case of specialized charts, the Earth is often drawn while not following the original form of projection, but with joined and irregular parts.The charts of this type are called stopped projections and include/understand the projection of Goode and the equivalent projection of Eckert.

5
Realization of a chart
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The most significant progress in the manufacture of the charts came from the techniques of remote collecting, i.e. techniques which truly gather data on an object without the touch, in particular the air photography (which includes/understands photography with infra-red) and photographs it by satellite.Total Positioning System (GPS) implements the triangulation by satellite, which reduced the margin of error considerably when it is a question of locating exactly points on the surface of the Earth.The recourse to the computer to draw charts counts among the most recent innovations

5.1
Observation

A chart rests essentially on a meticulous survey of the geographical sites and relations existing between a great number of points in the area considered.Today, almost all the original charts call upon the aerial observation in addition to the information obtained by the usual techniques of topography.The images obtained by satellite get a great number of precise information concerning the site of mineral deposits, the tentacular urban development, the penetration of the vegetation and the various types of grounds.

5.2 Compilation and reproduction

Once the data gathered, the chart must carefully be prepared according to its final destination so that all relevant information is communicated clearly and precision.The surveys and the photographs carried out are then used to enter a great number of points on a grid of cross lines which correspond to the projection chosen for the chart.The heights are indicated and the level lines, if they are used, are directly drawn from stereoscopic pairs of photographs.The roads, the rivers and the rivers are drawn according to the same process, as well as the site of the other elements of the chart.

The preparation of a chart for the impression starts with a series of sheets, at a rate of a sheet for each color used.These sheets are composed of a plastic covered with an opaque substance;the lines and the symbols are traced on surface using a sharp-edged instrument of engraving which removes the opaque layer, according to a technique which concerns the lithography.Each one of these sheets constitutes negative from which is carried out a lithographic plate.

There are also orthophotocartes, whose base is made up true photographs.The charts of this type are a mosaic of parts of carefully cut out air photographs, which were modified using a orthophotoscope to eliminate the deformations from scale and angle.It is possible to record information on the co-ordinates of a geographical area and on the distribution of the statistical phenomena of this zone.An instrument as a continuous graph plotter makes it possible a computer to carry out charts by using the recorded data.It is possible to post on a video screen the charts created by computer, which can be easily modified by an operator.The charts of this kind make it possible to provide an animated image of a change for one determined period, because the data of the chart and the later modifications are recorded.