September 21, 2006 – Until about 30 years ago, cartographers took hours, days or months to hand-draw maps. The mapmakers worked at drafting tables with pen and ink, T-squares and specialized tools for lettering and drawing shapes, or they used scribing techniques to cut or engrave line work into a special material used to make negatives.
Today, mapmakers sit in front of computers and use map-making software to produce automated and digitized maps. “Computer mapping has changed the whole world of cartography,” says Tanya Allison, Professor and Program Coordinator of Applied Geography at Montgomery College in Rockville. “It could take days to months to complete a map. Now, we can create a map within minutes.”
Ancient mapmakers used a global map coordinate system of longitude, latitude and elevation to make early maps of the Earth, says Richard Pearsall, a 30-year cartographer with the U.S. Geological Survey in Reston. The Greeks developed the concept of latitude and longitude in 150 B.C., he says.
“By the fact that the Earth rotates on its axis and revolves around the sun, the sun and stars appear to move across the sky on a known track,” Mr. Pearsall says. “Through observations of the sun and stars, mariners and explorers used precise equipment called a sextant and a precise timepiece called a chronometer that was synchronized with a master clock in Greenwich, England, to accurately measure their latitude and longitude on the Earth.”
In 1884, more than 25 nations adopted a standard for latitude and longitude and selected Greenwich as the location for the zero longitude line, Mr. Pearsall says. “Even though equipment and techniques have evolved over time, the basic premise of mapping has not changed since the days of the ancient mariner,” Mr. Pearsall says.
Mapping requires converting the three-dimensional form of Earth’s curved surface to two dimensions. A process called data projection uses mathematical calculations to make the conversion and flatten Earth’s surface onto paper. Cartographers have developed hundreds of projections or grid systems to represent Earth and its continents in circular, square, conic and other shapes.
Cartographers use these grid systems as the foundation to begin building maps, such as reference maps, political maps that indicate boundaries, physical maps that show some of the features of the Earth’s surface, and thematic maps that provide data to analyze phenomena such as economic changes and population growth.
The cartographer making a map has to determine the area to be mapped, the message to be imparted and the sources that can provide the information, says John Hebert, Chief of the Geography and Map Division of the Library of Congress. “That information has to be made into geographic reality,” Mr. Hebert says. “There has to be an agreement of what the intention of the map is, and that varies with each map.”
Initially, cartographers had to rely on ground-survey data to generate data for maps. However, as technology progressed from hot-air balloons to airplanes to satellites and, most recently, to Global Positioning Systems (GPS), cartography could incorporate the use of aerial photography, satellite images and remote sensing for additional data sources, Mr. Pearsall says.
With the advent of computers, cartographers in the 1970s and 1980s began using crude map-making software for statistical data. In the 1980s and into the 1990s, they used a tool called a digitizing table to convert cartographic data into digital form. They placed a paper map onto the table, which has a precise electronic grid built into it, and traced the data with a special digitizing tool, similar to a computer mouse, to transfer the data into digital form.
Cartographers digitized maps in layers, putting in one type of information at a time, such as political boundaries, transportation networks, buildings and structures, elevation, vegetation, and hydrography, which includes rivers, lakes and other bodies of water.
“Today, you can pretty much find anyplace you need to map in digital format, or you can scan it in or download it from an existing file,” Ms. Allison says. Computer scanners have, for the most part, replaced the digitizer, Ms. Allison says. A map can be scanned in and updated, such as with new roads in a developing area.
Cartographers use map-making software, such as Geographic Information Systems (GIS) software, to create a new map or alter and update an existing one. They build the data they plan to put into the map, such as bodies of water and roads, in separate layers or files. “That way they are able to add and delete or extract information as needed, and it also allows them the opportunity to share information among agencies,” Ms. Allison says. If the information does not already exist, cartographers can create their own layer by inputting the data points they collected, such as the beginning, middle and end points marking the location of a river or road, says Daniel Cole, GIS Coordinator for the Smithsonian Institution. The cartographers can add data taken from satellite imagery, aerial photography and GPS receivers, or they can use existing environmental data sets from government and private databases, he says.
The data entered into a map is represented by points, lines and polygons to indicate geographic features, such as a water tower (point), river or road (line) and the boundaries of a state (polygon), says David Rain, assistant professor of geography and international affairs at George Washington University. “You’ve taken apart the elements of a map and simplified them into a language the computer can understand,” says Mr. Rain, who holds a doctorate in geography. “It’s just making a simplified model of the world that the computer can restore, analyze, retrieve when needed and overlay with other analyses.”
Making maps involves making hundreds of decisions, says Allen Carroll, chief cartographer for the National Geographic Society. Cartographers, for example, have to decide what color schemes, patterns and symbols to use and which features to include, he says. “One of the most important decisions to make is to figure out what doesn’t go on the map. A map that is too crowded with stuff becomes unreadable,” he says. As Ms. Allison says, “Cartographers need to understand the purpose and audience of the map to develop a good product.”