Maps and Mapping

Summary

Mapping encompasses methods for representing geospatial information in paper and digital forms, as well as the use of other technologies, such as remote sensing and geographic information systems (GIS). Maps are needed in areas ranging from civil engineering and regional planning to navigation, and geospatial data is increasingly valuable for analysis in business, government, and beyond. Computer technologies and the Internet have brought profound changes to how maps are created and used, and a growing number of mapping applications have been developed for portable devices, such as car navigation systems and smartphones.

Definition and Basic Principles

Maps assume many forms, including spherical globes, folded paper charts, wall-sized murals, and images displayed on tiny electronic screens. As symbolic representations at varying scales, maps show a selection of information, including some components of space. The most well-known map form is a geographic two-dimensional depiction of a three-dimensional area for means of orientation, as in the standard road map. However, maps may also be three-dimensional, be interactive, or present much more abstract spaces or concepts. In addition to describing features on the Earth's surface, maps can represent underwater areas, the interiors of caves, celestial bodies like planets, the structure of DNA, or the relationships between the characters in a work of fiction, among many other examples. The term "cartography" refers to creating maps and related geographic products. According to the International Cartographic Association, cartography is the art, science, and technology of making maps.

Maps can be divided into two general categories: general-purpose and thematic maps. General-purpose maps various information, commonly including lakes, rivers, roads, cities, and administrative or political boundaries. Most general-purpose maps, such as road and topographic maps, are designed to serve as reference tools. In contrast, thematic maps show patterns and distributions corresponding to a single topic or theme, such as rainfall or corn production.

Background and History

For more than four thousand years, maps have been used to record and communicate information about the Earth. The ancient Greeks created maps to characterize the Earth's spherical shape, while legions of Roman soldiers used them as tools in the conquest of new territories. Drawn by hand, early maps showed landscape features using pictorial symbols to represent mountains, rivers, and other physical features. Later technologies, such as printing, eliminated the need for maps to be painstakingly copied and increased the speed at which maps could be reproduced and disseminated. Exploration, especially during the fifteenth and sixteenth centuries, created a demand for maps to assist in ocean navigation and to document newly discovered locations.

Modern maps play many societal roles, from guiding aircraft to providing reference information within school textbooks. Under most circumstances, maps are superior to charts and graphs in their ability to represent distances, directions, and the relative sizes of objects over space. In addition to showing the locations of features, maps can efficiently represent geographic patterns and the spatial extent of physical entities, such as rivers and mountains. They are also useful for showing cultural features, such as property boundaries and political or administrative areas. As archives of spatial information, maps are used extensively to record the locations of historical events and spatially referenced scientific data. In addition to their use in storing information, maps serve as important research tools for visualizing geographic data needed for evaluating hypotheses about spatial distributions. The development of computer technology allowed GIS and other mapmaking tools to drastically increase the power and potential applications of maps and mapping.

How It Works

Scale and Projection. All maps of the Earth's surface require some level of reduction. Map scale is an important concept to maps and mapping because it determines the level of map reduction necessary. Scale is the ratio of a distance measured on a map to the distance it represents in the real world, using the same units of measurement. For example, one inch measured on a map with a scale of 1:24,000 represents 24,000 inches (or 2,000 feet) in the real world. The scale used on any given map determines the size of the area that can be represented as well as the level of detail that can be depicted. In addition to the representative fraction (for example, 1:100,000), the scale can be shown using a verbal statement such as "one inch equals one mile" or a graphic or bar scale printed directly on the map.

Cartographers distinguish between small- and large-scale maps. Small-scale maps represent very large areas of the world and are useful for representing entire countries, continents, or the globe. In contrast, large-scale maps can show very small areas at higher levels of detail. City road maps and topographic maps are examples of large-scale maps. Given that geographic mapmaking involves reductions, the cartographer must choose the features to be shown and the symbols used to represent those features. This process, called selection, must be closely tied to the map's purpose. In addition, complex objects, such as coastlines, must be simplified to reduce unnecessary detail.

While most maps use a single scale, some may vary throughout to achieve the desired effect. Others intentionally distort scale, whether to simplify use (as in many subway maps that stylize the train lines to improve readability) or to emphasize a point (such as a cartogram that displays countries' sizes based on population).

Another important consideration is the choice of projection for displaying mapped information. Projection is a mathematical transformation of geographic information from the spherical Earth to a flat or undeveloped surface. Because spherical surfaces cannot be flattened without distortion, the cartographer must select the most critical properties to maintain during this transformation. For example, on a world map, it may be desirable to keep the relative sizes of countries to make comparisons. Although retaining the property of equivalence, this type of projection distorts the shapes of countries near the poles. The well-known Mercator projection, first published in 1569, is helpful for ocean navigation because it preserves shapes and lines of constant geographic direction as straight lines. However, a disadvantage of the Mercator projection is that it severely distorts the relative sizes of polar areas, making the island of Greenland in the North Atlantic look larger than the continent of South America, which is fifteen times larger than Greenland.

Geographic Grids. Cartographers use geographic grids, or coordinate systems, to place points, lines, and areas to systematically organize geographic information. Most maps are created using either the latitude and longitude coordinate system or a rectangular coordinate system. Latitude-longitude and rectangular grids use Cartesian coordinates (x, y). The point where the prime meridian (0 degrees longitude) and the equator (0 degrees latitude) cross is an origin against which all other locations are referenced. Smaller geographic areas are often mapped with rectangular coordinates that use an origin located outside and to the southwest of the area of interest to make all coordinate values positive.

Map Design. Map design is a systematic process involving selecting and arranging map elements to facilitate a user's correct interpretation of ideas and concepts. Cartographic design has benefited from developments in both graphic design and cognitive psychology. Because the principal objective of mapmaking is communication, cartographers need to select visual elements and arrangements that present concepts and spatial relationships in ways that the viewer can easily interpret. The design process can require several stages as alternatives are tested and modified. Basic graphic elements manipulated in the design process include points, lines, and area symbols. In addition, the selection and placement of text is an important design element. As French cartographer Jacques Bertin suggested, graphic elements used in cartography can be made more or less prominent through changes in hue (color), value (darkness or lightness), texture, orientation, size, and shape. Design is affected by the choice and design of symbols and the arrangement of map elements. In the design process, cartographers must be careful to use space efficiently and to avoid symbols that create unwanted attention or noise. Other vital concepts within map design include achieving balance in the arrangement of map elements and creating a visual hierarchy that draws the map reader's attention to features most important to the map's purpose.

Map Output. Developments in map reproduction have followed innovations in printing, beginning with the invention of the printing press by Johannes Gutenberg in 1440. Early printing technology employed a process called letterpress, in which ink was applied to raised portions of wooden blocks pressed against paper. Introduced in the early 1700s, engraving involved the application of ink to depressions in a metal printing plate. Engraving improved map reproduction because it enabled finer line widths and improved gray tones and patterns. Lithography, a printing technique based on the incompatibility of grease and water, was introduced in the 1800's. Most modern paper maps are reproduced using lithographic plates, which are applied to a rotating drum to transfer an image to a moving sheet of paper. Four-color maps use lithographic plates corresponding to the subtractive primary colors of cyan, magenta, and yellow plus black. A wide variety of colors can be created by combining percentages of each primary color. Modern printing presses use computer files to create plates needed to produce color maps, with sheets of paper passing through the press once for each plate.

Maps can also be reproduced in smaller quantities using low-cost output devices, such as laser printers and ink-jet plotters. Electrostatic (or xerographic) copying is a common reproduction method. Laser and ink-jet printers have also become a popular method for reproducing small numbers of maps. The readability of map lettering and the sharpness of lines and gray tones are functions of the printer's resolution as represented in dots per inch (dpi). Low-end printers typically offer 300-dpi output, meaning each square inch has 90,000 dots. Higher-end printers and plotters offer resolutions exceeding 2,000 dpi.

The introduction of personal communications devices with high-resolution screens has led to an increasing number of maps that are never printed. These virtual maps may be used to check weather conditions or find a street address. Internet-based Google Maps has been an innovator in making virtual maps, aerial photographs, and satellite images accessible to the public. Google Maps and Google Earth enable the simultaneous viewing of aerial photographs and map information in the form of roads, contour lines, and political boundaries. Mapping tools enable the user to zoom in or out, pan in any direction, and select specific map features and points of interest to be displayed.

Computers and Mapmaking. The most significant change to cartography during the twentieth century was the introduction of computers that enabled tasks previously requiring hours to be carried out in seconds. Computer cartography, or the use of computers in map production, has been particularly beneficial in enabling cartographers to experiment. The cartographer can resize and reposition map elements, such as text labels, scale bars, and legend boxes, using mapping software. Computers also facilitate mathematical and statistical transformations of tabular data needed for making thematic maps. Some programs enable map images to be combined with other spatial data, such as aerial photographs or satellite images. Increasingly, digital databases are replacing paper maps as the principal method for storing and retrieving geographic information.

Before geographic information can be manipulated by a computer, it must be converted to a digital form. The process of capturing points, lines, and areas shown on a paper map in a digital format is called digitizing. Analog information can be digitized by tracing features of interest individually using a tablet or table-sized digitizer. Digitizing can also be accomplished by scanning an entire map sheet. Before scanned data are useful, they must be transformed into a system of coordinates, such as latitude and longitude. This process is called geocoding or georeferencing.

Applications and Products

Since 1985, most data used in computer mapping has been converted into digital format. For example, the United States (US) GeoData digital line graphs are computer files containing transportation and other line information captured from topographic maps maintained by the United States Geological Survey (USGS). The digital file set, called digital raster graphics, includes information scanned from USGS topographic maps. USGS digital elevation model data files contain grids of elevation values captured every thirty meters. They are useful for constructing contour maps, three-dimensional terrain diagrams, and computer simulations, such as aerial fly-bys.

Computer technology also makes it possible to create cartographic visualizations, such as animated maps. Maps that use a sequence of digital images are called temporal animations. This type of map is useful for representing changes over time, such as the movement of military fronts during a battle.

Computer technologies have influenced maps through developments in closely related fields, such as aerial photography, GIS, and remote-sensing satellites. Remote sensing involves the capture of information about the Earth using sensors and is commonly divided into photographic methods, such as aerial photography and nonphotographic imaging, which include sensors looking outside visible portions of the electromagnetic spectrum.

Digital orthophoto quadrangles (DOQs) have emerged as an important source of information for constructing maps. DOQs are aerial photographs in digital form that have been rectified (corrected) for camera distortion. In addition to serving as a source to extract the location of physical and cultural features, they can be used as background images for maps. Multispectral scanners used by Landsat and other satellites capture large amounts of data using scanners sensitive to narrow wavelengths of energy emitted from the Earth's surface. Such data can be useful for revealing information that cannot be seen in photographic images, including stress or disease in vegetation.

Radio detection and ranging (radar) is another nonphotographic imaging system for mapping surface features, underground areas, and atmospheric conditions. Radar uses transmitted energy reflected by objects and then captured and converted into an image. Imaging radar used on space shuttle missions has become an important source of elevation data used in various mapping applications. Light detection and ranging (lidar) is an innovation for mapping the Earth by measuring the properties of scattered light as it comes into contact with distant objects. Lidar images are created by measuring the time needed for laser pulses to reach the Earth's surface. Some applications for lidar include three-dimensional mapping of urban areas and assessments following natural disasters.

Careers and Course Work

College and university courses in cartography are most often taught within geography departments. Students seeking careers in the mapping sciences should complete college coursework in geography, mathematics, statistics, and technical writing. Depending on the type of maps they will produce, they may also take coursework in graphic arts, computer programming, physics, remote sensing, computer-aided drafting, database management, planning, or geology. Various agencies and organizations employ cartographers, GIS analysts, and remote-sensing specialists. The US Geological Survey employs cartographers to maintain paper and digital map products. Its National Imagery and Mapping Agency supports mapping and imagery needs for the military and policy making. The US Department of Agriculture's Natural Resources Conservation Service maintains the Soil Survey Geographic Database, a critical spatial data set defining soil boundaries within the US. The Central Intelligence Agency (CIA) provides mapping products used internally and by other intelligence agencies. State and local government agencies and private organizations also employ geospatial experts. State agencies produce road maps used for promoting tourism, and local government departments maintain property and planning maps. Private companies also create maps and proprietary data used in mapping. 

Social Context and Future Prospects

Maps and other cartographic products are important in areas ranging from civil engineering and planning to the humanities. For example, maps are used in weekly magazines, newspapers, and websites. People riding the bus systems or other methods of public transportation of a city rely on maps. Journalistic maps typically show the countries, cities, or accident sites that are the focus of news events. Maps occur in many aspects of life, from mapping the stars, creating chronological timelines, producing mind maps of concepts in a classroom, mapping genealogy, or navigating a website.

Transportation maps, such as nautical and aviation charts, are critical to the safe movement of ships and aircraft. Within the US, the National Ocean Service of the National Oceanic and Atmospheric Administration (NOAA) publishes four types of nautical charts: general, sailing, coast, and harbor charts. The Federal Aviation Administration (FAA) publishes several aviation charts, including the world aeronautical charts at a scale of 1:1,000,000 and sectional charts representing smaller areas in greater detail at a scale of 1:500,000. Nautical and aviation charts must be updated frequently to reflect changes that can affect safety. Transportation maps also include street and highway maps, road atlases, maps showing airline or train routes, and bicycle or walking trail maps.

Topographic maps show rivers, lakes, mountains, other surface features, and cultural features, such as roads, cities, levees, and towers. Elevations on topographic maps are shown using contours defined as lines that join points of equal elevation. Bathymetric or hydrographic charts are a related map type that uses lines to represent underwater depths. The US Geological Survey (USGS) maintains topographic maps and maps showing geological cross-sections, groundwater areas, earthquake faults, and seismically active areas. Geologic maps have many uses, from mineral exploration to civil engineering. Most geologic maps use colors, gray tones, patterns, and sometimes letter codes to represent different rock types. In addition to government agencies, energy and mining companies also maintain maps showing fossil fuels, mineral reserves, and areas with the potential to generate power using solar or wind energy.

Maps are essential for recording the location of property boundaries and for planning applications. Local government agencies maintain cadastral maps to show ownership boundaries as a basis for property taxes. This type of map is also important to insurance companies. Many local government planning agencies maintain maps showing the city or county's infrastructure, such as water resources, sewers, and electric and gas lines. City and regional planners use maps for zoning changes and to maintain 911 emergency response systems.

The NOAA's National Weather Service is the principal federal agency responsible for disseminating information about weather conditions. Forecasters and others use weather maps to monitor or predict atmospheric conditions, including temperature, precipitation, wind direction and speed, humidity, cloud cover, and anomalies, such as thunderstorms, hurricanes, and tornadoes. Weather maps may show a single parameter, such as surface pressure, or multiple types of information. Climate maps include some of the same information shown on weather maps but for more extended time frames. Examples include maps depicting monthly temperature highs and lows or average yearly rainfall.

The wide availability of the Internet has created possibilities for the publication of new types of mapping products, such as electronic atlases, which allow users to generate customized maps by selecting the data to be shown. Electronic atlases enable users to search place names, easily locate cities, and find other information. An added benefit of the Internet is its ability to incorporate updates as soon as new information becomes available. Mapping technology and its use continued to evolve as the twenty-first century progressed. Blockchain maps analyze cryptocurrency. Health maps play a role in evaluating health data and were especially important during the COVID-19 pandemic of the early 2020s. Maps are also used to analyze a person's social media connections.

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