Cartography involves the creation, production, and study of maps. Many cartographers are geographers who specialize in the combination of art, science, and technology to make and study maps. Some cartographers teach map-making skills and techniques, some design and produce maps, and some are curators of map libraries. All cartographers, however, focus on maps as the object of their study or livelihood. In other cases, biologists, economists, geologists, hydrologists, planners, and others can engage in cartography to summarize or analyze spatial data. Geologists, for example, produce highly specialized geologic maps to show the three-dimensional arrangement of rock types in an area.

A major change in cartography during the late twentieth and early twenty-first centuries has been the use of geographic information system (GIS) software to produce, store, and use maps. GIS software can be used to create custom maps that cover an area or portray features of specific interest to a user. For example, a map showing vegetation types can be placed over a shaded relief map of Earth’s surface to illustrate the relationship between biology and topography. GIS software can also be linked to computer simulations of processes such as flooding or earthquake damage to help communities develop emergency response plans. Digital maps can also be widely distributed using internet map servers that allow users to interactively explore a large map by scrolling and zooming.

What is a map?

A map is a two-dimensional representation of the spatial distribution of phenomena or objects. For example, a map may show the location of cities, mountain ranges, rivers, or types of rock in a given region. Most maps are flat, making their production, storage, and handling relatively easy. Maps present their information to the viewer at a reduced scale. They are smaller than the area they represent and use mathematical relationships to maintain proportionally accurate geographic relationships between points. Maps portray information by using symbols that are identified in a legend.

The history of cartography

References to surveying and mapping are found in ancient Egyptian and Mesopotamian writings. The oldest known map is of an area in northern Mesopotamia. The baked clay tablet, found near Nuzi, Iraq, dates from approximately 3800 BC. Fragments of clay maps nearly 4,000 years old have been found in other parts of Mesopotamia, some showing city plans and others showing parcels of land. Over 3,000 years ago, the ancient Egyptians were surveying the lands in the Nile Valley. They drew detailed maps on papyrus to use for tax purposes.

Chinese cartographers produced maps as early as 227 BC. Following the invention of paper about AD 100, cartography flourished throughout the Chinese empire. Chinese cartography continued to have its own distinctive style until the 1500s, when it began to be influenced by European cartography.

Although Chinese cartography followed certain standards, it was not based on the same scientific principles as European cartography. The Greeks developed many of the basic principles of modern cartography, including latitude and longitude, and map projections. The maps of Ptolemy, a Greek astronomer and mathematician who lived in the first century AD, are considered the high point of Greek cartography. Although his maps appear crude by current standards, they are amazingly accurate given the extent of geographic knowledge at the time.

Cartography came to a near-halt in Europe during the medieval period, when maps were little more than imaginative illustrations for theological texts. In Muslim countries, however, the science of cartography continued to grow, and various techniques were refined or improved by Arabic cartographers. Their knowledge and skills were introduced into Europe during the Renaissance.

The eras of exploration that followed the Renaissance supplied cartographers with a wealth of new information, which allowed them to produce maps and navigation charts of ever-increasing accuracy and detail. Europeans became fascinated with the idea of mapping the world. The French initiated the first national topographic survey during the 1700s, and soon other European countries followed suit. Today, most countries have an official organization devoted to cartographic research and production.

Types of maps

There are many different types of maps. A common classification system divides maps into two categories: general and thematic. General maps are maps that show spatial relationships between a variety of geographic features and phenomena, emphasizing their location relative to each other. Thematic maps illustrate the spatial variation of a single phenomenon or variable, or the spatial relationship between two particular phenomena or variables, emphasizing the pattern of the distribution.

Maps can be either general or thematic, depending on the intent of the cartographer. For example, a cartographer may produce a vegetation map showing the distribution of various plant communities. If the cartographer shows the location of various plant communities in relation to a number of other geographic features, the map is properly considered a general map. The map is more likely to be considered thematic if the cartographer uses it to focus on something about the relationship of the plant communities to each other, or to another particular phenomenon or feature, such as the differences in plant communities associated with changes in elevation or changes in soil type.

Some examples of general maps include topographic maps, planimetric maps, and charts. Topographic maps depict the form of Earth’s surface, most commonly expressed as elevation above sea level, and are general maps if they also include features such as cities, rivers, and roads. Bathymetric maps depict underwater topography. Planimetric maps show features such as cities and roads without depicting elevations. Charts are used by the navigators of aircraft and seagoing vessels to plot positions and courses. World maps on a small or medium scale showing physical and cultural features, such as those in atlases, are also considered general maps.

Although the subject matter of thematic maps is nearly infinite, cartographers use common techniques involving points, lines, and areal units to illustrate the structure of spatial distribution. Isarithmic maps use lines to connect points of equal value; these lines are called isopleths, or isolines. Isopleths are used to show how certain quantities change with location and those used for a particular purpose may have a particular name. For example, isotherms connect points of equal temperature, isobars connect points of equal air pressure, and isohyets connect points of equal precipitation. Isopleths indicating differences in elevation are called topographic contour lines, and a topographic map that does not depict general features such as cities and roads would be a thematic map.

A topographic map is a good example of how isopleths are used to present information. Topographic maps use isopleths called elevation contour lines to indicate the topographic relief. Each contour line connects points of the same elevation, and the difference in elevation between each contour line is known as the contour interval. A contour interval of 20 ft (6.1 m) means that there is a 20 ft (6.1 m) difference in elevation between the points connected by one contour line and the points connected by an adjacent contour line. Closely spaced contour lines represent steep slopes and widely spaced contour lines represent gentle slopes. Closed contour lines, for example in the general shape of a circle or ellipse, represent hills.

Chloropleth maps are another type of thematic map. They use areas of graduated gray tones or colors to show spatial variations in the magnitude of a phenomenon.

Geographic illustrations

There are many portrayals of geographic relationships that do not qualify as maps as previously defined. Throughout human history, people have been illustrating geographic relationships between various elements of the physical and cultural environment. These geographic illustrations and representations are often beautiful, and can illustrate the worldview of the culture that produced them. Some are extremely accurate in their representation of geographic relationships. Most geographic illustrations, however, are not considered true maps by modern cartographers because they do not use a scale based on distance. The development of the tools and techniques for accurately measuring distance requires a particular technical and scientific world view not shared by all cultures.

Many geographic illustrations or representations do not have a scale. Those that do, typically have a scale based on traveling times. Traveling times for the same distance can vary depending on the nature of the terrain, weather conditions, or other variables. For example, a 4-mi (6.4 km) journey across rugged mountains in a snow storm and a 12-mi (19.3 km) journey across a relatively smooth plain on a spring day may both take eight hours. A geographic illustration using a time-based scale would show two equal intervals; a distance-based scale would show the 12-mi journey as three times longer than the rugged 4-mi trek. Clearly, for a nomadic or migratory society, a geographic representation with a scale based on traveling times would be extremely useful, whereas one with a scale based on a distance would be of little or no use.

Map making

Cartographers traditionally obtained their information from navigators and surveyors. Explorations that expanded the geographical awareness of a map-making culture also resulted in increasingly sophisticated and accurate maps. Today, cartographers incorporate information from aerial photographs and satellite images in the maps they create.

Modern cartographers face three major design challenges when creating a map. First, they must figure out how to represent three-dimensional objects in two dimensions. Second, cartographers must represent geographic relationships at a reduced size while maintaining their proportional relationships. Third, they must select which pieces of information will be included in the map and develop a system of generalization that will make the information presented by the map useful and accessible to its readers. This includes the development of symbols that will effectively convey the subject of the map.

Showing three-dimensional relationships in two dimensions

When creating a flat map of a portion of Earth’s surface, cartographers first locate their specific area of interest using latitude and longitude. They then use map projection techniques to represent the three-dimensional characteristics of that area in two dimensions. Finally, a grid, called a rectangular coordinate system, may be superimposed on the map, making it easier to use.

Latitude and longitude

Distance and direction are used to describe the location of an object in space. In conversation, terms like right and left, up and down, or here and there are used to indicate direction and distance. These terms are useful only if one knows the location of the speaker; in other words, they are relative. Cartographers, however, need objective terms for describing location, because maps are intended for use by many individuals in many different situations. The system of latitude and longitude, a geographical coordinate system developed by the Greeks, is used by cartographers for describing location.

Earth is a spheriod rotating around an axis tilted approximately 23.5 degrees. The two points where the axis intersects Earth’s surface are called the poles. The equator is an imaginary circle drawn around the center of Earth, equidistant from both poles. A plane that sliced through Earth at the equator would intersect the axis of Earth at a right angle. Lines drawn around Earth to the north and south of the equator and at right angles to Earth’s axis are called parallels. Any point on Earth’s surface is located on a parallel.

An arc is established when an angle is drawn from the equator to the axis and then north or south to a parallel. Latitude is the measurement of this arc in degrees. There are 90 degrees from the equator to each pole, and sixty minutes in each degree. Latitude is used to determine distance and direction north and south of the equator.

Meridians are lines running from the north pole to the south pole, dividing Earth’s surface into sections, like those of an orange. Meridians intersect parallels at right angles, creating a grid. Just as the equator acts as the line from which to measure north or south, a particular meridian, called the prime meridian, acts as the line from which to measure east or west. There is no meridian that has a natural basis for being considered the prime meridian. The prime meridian is established by international agreement and currently runs through the Royal Observatory in Greenwich, England. Longitude is the measurement in degrees of the arc created by an angle drawn from the prime meridian to Earth’s axis and then east or west to a meridian. There are 180 degrees west of the prime meridian and 180 degrees east of it. The international dateline lies approximately where the 180th meridian passes through the Pacific Ocean.

Using the geographical coordinate system of latitude and longitude, any point on Earth’s surface can be located with precision. For example, Buenos Aires, the capital of Argentina, is located 34 degrees 35 minutes south of the equator and 58 degrees 22 minutes west of the prime meridian. Anchorage, the capital Alaska, is located 61 degrees 10 minutes north of the equator and 149 degrees 45 minutes west of the prime meridian.

Map projections

After locating their area of interest using latitude and longitude, cartographers must determine how best to represent that particular portion of Earth’s surface in two dimensions. They must do this in such a way that minimal amounts of distortion affect the geographic information the map is designed to convey.

In order to understand the difficulty of such a task, imagine an orange with lines similar to parallels and meridians inked onto its surface. Now imagine removing the peel from the orange in one piece. If the peel of an orange is laid out flat on a tabletop, the peel will crack and break in various places. The cracks and breaks will distort the original shape of the orange, and the inked lines will no longer bear the same spatial relationship to each other as they did when the peel was on the orange. If the peel is arranged so that there are no cracks, breaks, or distortions in the relationships between the lines on its surface, the peel will assume the shape of a hollow sphere. There are only two choices: a spherical, distortion-free arrangement or a flat, distorted arrangement.

Cartographers have developed map projections to transform geographic information from a spherical surface onto a planar surface. A map projection is a method for representing a curved surface, such as the surface of Earth, on a flat surface, such as a piece of paper, so that each point on the curved surface corresponds to only one point on the flat surface.

There are many types of map projections. Some of them are based on geometry; others are based on mathematical formulae. None of them, however, can accurately represent all aspects of Earth’s surface. Inevitably there will be some distortion in shape, distance, direction or area. Each type of map projection is intended to reduce the distortion of a particular spatial element. Some projections reduce directional distortion, while others try to present shapes or areas in as distortion-free a manner as possible. The cartographer must decide which of the many projections available will provide the most distortion-free presentation of the information to be mapped.

Rectangular coordinates

Although the geographical coordinate system is useful for large areas, it can be awkward to use for small areas. Many city maps use rectangular coordinate systems. After the map is complete, a grid is superimposed over it. The horizontal lines of the grid are assigned one set of numbers or letters, the vertical lines are assigned another set of numbers or letters. An index of place names is generated, which lists the horizontal and vertical coordinates for each place shown on the map. Used in conjunction with an index of place names, the rectangular coordinate system makes it simple for map readers to locate particular places. The Universal Transverse Mercator (UTM) system divides most of Earth’s surface into zones, each of which has its own rectangular grid system. Most global positioning system (GPS) receivers can be set to show locations in UTM coordinates. Within the United States, each state has its own rectangular coordinate system that is used for surveying and construction.

Reducing size while maintaining accurate proportions

Maps present geographical information at a reduced scale. In order for the information to be useful to the map user, the relative proportions of geographic features and spatial relationships must be kept as accurate as possible. Cartographers use various types of scales to keep those features and relationships in the correct proportion.

Scale is the mathematical relationship between a distance between two points on the map and the distance between two corresponding points on the ground. The relationship is expressed as a ratio, the first number being the distance between two points on the map and the second number being the actual distance represented. The number indicating map distance is always one. Thus, a map with a scale of 1:125,000 tells the map user that every unit of distance on the map equals 125,000 of the same units of distance on the ground. The units of distance used are not important as long as they are the same on both sides of the ratio. One centimeter on the map would equal 125,000 cm on the ground, 1 ft on the map would equal 125,000 ft on the ground, and 1 m on the map would equal 125,000 m on the ground.

Maps showing a large area are called small-scale maps. This is because the ratio between map distance and actual distance is a small number. The number is small because one distance unit on the map represents a large number of distance units on the ground. For example, a map showing North America at a scale of 1:40,000,000 would use one unit of map distance to depict 40,000,000 units of actual distance. One centimeter on these maps equals 40 km of actual distance. Such a map fits on a piece of paper only 9 in wide and 8.25 in high (23 cm by 21 cm).

Maps showing a small area are called large-scale maps. The ratio between map distance and actual distance is a large number. It is large because each unit of distance on the map represents a relatively small number of distance units on the ground. City maps are good example of large-scale maps. A city map of Portland, Oregon with a scale of 1:38,000 fits on a piece of paper 41.75 in by 35.5 in (106.5 cm by 90 cm). One centimeter on this map equals 0.38 km of actual distance and one inch equals six tenths of a mile.

Every properly prepared map has a statement of its scale. This statement can take many forms, and many maps express scale in more than one way. The scale may be indicated by a ratio, such as 1:100,000 or 1/100,000 (the latter is less common). This ratio is called the representative fraction. Representative fractions are not particularly easy to use in everyday situations, so cartographers have developed other ways to communicate the scale of a map to its users.

Sometimes cartographers use a graphic scale, also called a bar scale. A graphic scale is a line or bar subdivided to show how many actual miles fit into a particular measurement on the map. In most parts of the world the graphic scale shows how many actual miles or kilometers are represented by a particular number of inches or centimeters on the map.

Two other means for expressing scale are the area scale and the verbal statement. Area scales are used for maps based on equal-area projections, that is, maps that present all areas shown in the same proportion to one another as they occur on Earth’s surface. These scales tell the reader that one unit of area on the map represents a certain area on the ground. The scale can be written 1:250,000², although 1:250,000 is more common. The latter expression assumes the reader is aware that the number represents a ratio of square units. A verbal statement of scale uses words, rather than numbers or graphic symbols. “One inch equals one mile” is a verbal statement of scale equivalent to the representative fraction 1:63,360 (there are 63,360 inches in one mile).

Presenting geographic information effectively

No single map can accurately show every feature on Earth’s surface. There is simply too much spatial information at any particular point on Earth’s surface for all of the information to be presented in a comprehensible, usable format. In addition, the process of reduction has certain visual effects on geographic features and spatial relationships. Because every feature is reduced by the ratio of the reduction, the distance between features is reduced, crowding them closer together and lessening the clarity of the image. The width and length of individual features are also reduced.

When designing a map, cartographers strive for clarity and effective communication. They use the technique of selection to determine which pieces of information to include and what kinds of symbols will most effectively portray that information.

A wide array of geographical information is available to mapmakers. When preparing a map, cartographers must choose only those pieces of information that are pertinent to the purpose of the map and then display those pieces of information in a way that effectively communicates their significance. Only information deemed significant or useful is selected for inclusion in the map.

Once cartographers have selected the information that will be portrayed on the map, the information must be displayed in an effective manner. Cartographers deal with this problem by applying the techniques of cartographic generalization. Both map geometry and map content are generalized.

Geometric generalization techniques change the placement and appearance of various map features in order to make the map easier to interpret and more pleasing to the eye. For example, not every twist and turn of a 15 mi stretch of river can be accurately portrayed at a 1:500,000 scale, where 1 in equals 7.89 mi. The path of the river is simplified, reducing excessive detail and angularity. A railroad running 50 ft from the river would appear to run in the riverbed when shown at a 1:500,000 scale. Using cartographic generalization, the cartographer displaces the railroad, showing it next to the river, avoiding graphic interference and increasing the readability of the map. The numerous right-angle bends in a highway following rural property boundaries along the river would be smoothed by the cartographer, reducing their angularity and thereby making the line of the highway easier for the eye to follow.

Linear and areal features can be generalized using the techniques of simplification, displacement, smoothing, and enhancement. Additionally, the techniques of dissolution, segmentation, and aggregation are applied to areal features. Point features are generalized by displacement, graphic association, and abbreviation.

Map content is generalized using the technique of classification, in which similar features to be grouped together are represented by a single symbol. Campgrounds, for example, are often represented by a tent-shaped symbol, even when the facilities can accommodate trailers or large recreational vehicles. Categorization is another form of classification. Many maps, for example, use one point symbol for population centers of 1,000–10,000. Another point symbol for population centers of more than 10,000 but less than 100,000, and a third point symbol for population centers of more than 100,000 but less than 500,000. Cartographers must carefully consider the implications of such classification schemes. The system described above implies that towns of 1,000 and towns of 9,000 have more in common than towns of 9,500 and towns of 10,500.

Cartographic production

For many centuries maps were produced entirely by hand. They were drawn or painted on paper, hide, parchment, clay tablets, and slabs of wood, among other things. Each map was an original work; the content may have been copied, but each map was executed by hand.

Once printing techniques were developed, many reproductions could be made from one original map. Chinese printmakers were producing maps on handmade paper using wood block printing techniques over 1,800 years ago. The Europeans developed the printing press and movable type in the 1400s, and maps became more common and more accessible. The paper they were printed on was still handmade, however, and any colored areas on the map had to be painted by hand.

The introduction of the lithographic printing method in the late 1800s allowed multi-colored maps to be produced by machine. Various photographic techniques were integrated into the printing process during the last 200 years, increasing the variety of scales at which maps were produced. Despite these production advances, each original map was still drawn by cartographers, using technical pens, various lettering devices, straight edges and razor knives, the traditional tools of the trade.

During the last few decades, cartographers have acquired another production tool, the computer. They use the computer to conjure and produce map images, but computer programs cannot replace cartographers. The various techniques for cartographic expression involve a sense of craft and artistry that has not yet been duplicated by electronic means.

Key Terms

Isopleth— A line connecting points of equal value.

Latitude— The measurement in degrees of the arc created by an angle drawn from the equator to Earth’s axis and then north or south to a parallel.

Longitude— The measurement in degrees of the arc created by an angle drawn from the prime meridian to Earth’s axis and then east or west to a meridian.

Map— A generalized two-dimensional representation of the spatial distribution of one or more phenomenon or objects presented at a reduced scale.

Map projection— The geometric or mathematical methods for representing portions of the curved surface of a sphere as a flat surface so that any one point on the sphere corresponds to only one point on the flat surface.

Relief— The difference in elevation of various parts of Earth’s surface.

Representative fraction— A numerical expression of map scale that gives the ratio between any distance on the map and the corresponding distance on the ground.

Scale— The mathematical relationship between a distance on a map and the corresponding distance on the ground.