Spatial Technologies-The Art of Cartography

How GIS shapes map-making.

Cartography, The Study and creation of maps, has long been a marriage of art and science. A map is a visual representation of a place, and its principal task is to communicate information. It can show the real world—past, present or future—and can even illustrate an imaginary world. Maps also have been instrumental in allowing us to explore parts of our world. Centuries ago, sailors used early maps to navigate the globe, and pioneers used rough hand-drawn maps to locate mountain passes on their way west. More recently, we use maps to help us get around town or to travel from one place to another.

Cartography has come a long way since the days of Johannes Gutenberg's printing press, woodcut maps, cooper engraving and scribing. Digital map creation and publishing tools simplify the process of generating high-quality maps, with GIS being at the forefront. Advances in GIS technology have dramatically changed the art of making maps.

Basics of GIS Map-making

The ability of GIS programs to produce high-quality maps has improved significantly in the last couple of years. It's much quicker, easier and affordable to update maps than ever before. Cartographers can produce more accurate maps without sacrificing quality.

Many organizations that produce maps are already using GIS in one form or another. These groups include U.S. Geological Survey, National Geospatial-Intelligence Agency, Ordinance Survey in Great Britain, Rand McNally, National Geographic Society and Automobile Club of America. All produce a wide variety of traditional paper maps as well as online maps.

For cartographers, the geodatabase is the core of map-making. A geodatabase provides the framework to manage the data needed to produce maps. The ability to directly link data to objects on a map has had a revolutionary impact on cartography.

With a geodatabase, there's a system that can integrate information from surveying, geoprocessing, satellite imagery and other data sources. Digital information can be stored in an open database so multiple users can access it, and updates are fairly easy. That helps ensure that future maps have the most current information available. The real benefit of GIS is that maps are intelligent—each map created is connected to a geodatabase that contains information about attributes and relationships.

Although there are many different types of maps, they all share certain similarities. Maps graphically depict a representation of a place, show a scale that relates the illustration on the map with a real length or distance and include a legend that explains symbols and patterns used in the map.

Maps are the most common products of a GIS program, and virtually all GIS programs provide the essential tools needed to make maps. Some GIS developers have identified cartography as an important focus area. ESRI, for example, has incorporated a wide range of cartography tools in its software.

The usefulness of a map depends on our ability to interpret the information presented. Cartographers must decide what features to display on a particular map to communicate the right information. Does a road need to be conveyed as double white lines with a yellow centerline, or does a single thick line convey the appropriate information?

A primary principle used in map-making is the concept of generalization, which involves simplifying data so the map is more readable. Too much information on a map is visually confusing and makes it difficult to understand. The content and level of detail in a map must change depending on scale.

For a recent project, I wanted to build a map showing Cape Cod. The problem is that most of the data sent to me by the client was very specific. For example, there were hundreds of color digital ortho quads at a resolution of less than half-a-meter resolution. It was much more detail than I needed—I would've preferred more generalized information at about 15-meter resolution because it would have been much easier to work with.

Being able to generalize detailed information requires a sophisticated level of spatial analysis. ESRI has been working on pattern recognition to help sort through highly detailed data and extract the information needed to create a map at a different scale. ArcGIS 9.2 will incorporate four new generalization tools: simplify polygon, simplify building, aggregate polygons and collapse to centerline. Previously these features were available only in ArcInfo Workstation.

Automating the Process

The trend in GIS programs is to provide high-quality automated symbolization while providing the cartographer the option to override this process to customize the appearance of an individual map.

Cartographers want to take advantage of the freedom and flexibility that drawing and editing tools provide, while also using automated geoprocessing tools to build the foundation of a map. Map templates, for example, help automate the process of creating maps. Automating many of the basic tasks associated with creating a map allows cartographers to spend their time on the more artistic parts of their craft.

One problem with automation, though, is that the final graphic results are sometimes less than desirable. Most GIS users have created maps where some text labels overlap or are unreadable. This is a problem because readability is critical to the success of any map. As a result, cartographers must be able to tweak an image to achieve a specific result and to communicate information.

Critical Symbols

Symbolization is critical to creating readable maps. All maps are basically abstractions of reality, and they use symbols to illustrate different elements and features. Your GIS program needs to provide a rich set of tools for creating, modifying and applying different types of symbols. Most GIS programs offer a comprehensive set of graphics and symbols, including multiple map areas, legends, north arrows, titles, text blocks, geometric shapes, patterns and so forth.

Most GIS programs let you access premade symbols, edit these symbols, add symbols from other programs and even create your own images from scratch. Premade symbols are nice because they greatly reduce the time needed to produce a map. Most GIS programs provide extensive libraries of common symbols, lines and patterns. ArcGIS, for example, comes with more than 12,000 premade symbols grouped by themes. We tend to create a lot of our own symbols, in part so that our maps will have a different graphic character than maps produced by others. For a recent master-planning project, we created a custom symbol using ArcSketch to help us simplify the time it takes to generate design concepts.

Text and Labels

Text is a major part of any map. Despite significant improvements in tools for text placement, labeling a map is still a difficult process. Frequently, the labels automatically generated with geospatial data overlap, cover up important data or are arranged in a confusing way. When creating maps, I spend a lot more time manually laying out text than I would like.

Cartographers need text tools that allow them to control fonts, paragraph and character styles, paragraph composition, underline and strikethrough, transparent effects and more. TrueType, Adobe Type 1 (PostScript fonts) and OpenType are among the most common font types, and many GIS programs support all three. This minimizes the need for font substitutions, which can dramatically change the visual appearance of a map.

Most maps include labels to identify key features such as roads and significant natural features. There are exceptions, of course—for one project in Alabama, our client requested a map showing all of the natural features, but wanted to eliminate anything that would detract from the visual character of the map, so no labels were included (figure 1).

Figure 1. For this map showing Lake Martin in southern Alabama, we avoided labels and manmade features because the emphasis was on the landforms and natural features of the region.

Adding Illustrations

One complaint I frequently hear is that maps generated via GIS programs lack the visual quality of those created in dedicated map-making or illustration programs. We frequently use GIS to develop the basics of our maps, but then use an illustration program such as Adobe Illustrator, CorelDraw, Micrografx Designer and Macromedia Freehand to add the final graphic details. These programs are designed to support artistic expressions and are used for a wide range of graphics and illustrations, including logos, brochures, newsletters, reports and advertisements, as well as maps.

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I haven't found a GIS program that has drawing and layout tools of a program like CorelDraw or Illustrator. CorelDraw, for example, includes smart drawing tools that recognize shapes while you are drawing, tools for text layout, dynamic guides to help with layout and design, creative tools for generating different image effects, trace tools for converting raster images into shapes and an eyedropper tool that is able to copy the properties from one object to another with just one click of a button. Illustrator has a Live Paint function that lets users apply color to any area of a map or drawing and use overlapping paths to create new shapes (figure 2). This tool is perfect for creating conceptual bubbles on a map. Adobe Streamline and Corel OCR Trace can be used to extract vector images from scanned photographs and maps.

Figure 2. Adding hill shades and other geoprocessing techniques available via GIS can add a sense of depth and enhance the visual quality of the final map.

The problem with graphically touching up a map by hand is that automatically updating data is not possible. As a result, many cartographers would prefer to create their entire map within one GIS program. This approach would reduce costs by eliminating the need to purchase additional software, and it would improve efficiency because all work could be done within the same program. Many of the drawing tools currently being added to GIS programs are based on the freeform drawing and editing tools found in these illustration programs.

Map Production

There are two major components of map making: the creation of a map and the production of the completed map. To meet customer demands, mapping agencies must be able to produce vector and raster data products as well as traditional paper maps. The Internet is being used more and more to share GIS maps, and that trend is expected to continue. A Web-based approach helps automate the production of solutions-based maps that can be customized by individual users. But for all of the advantages of Web-based mapping, traditional cartographic paper maps are still popular.

Creating quality maps for interactive viewing and distribution on the Web requires a significantly different philosophical approach. For one thing, the resolution you have to work with is limited, so graphic user interfaces are as much a part of the cartographic process as is the creation of the map.

One common problem is that GIS maps printed on oversized paper are inadequate for presentation to a large audience. We often reprint these maps onto 11" X 17" sheets and hand them out to audience members. Another approach is to use an overhead projector, but even the best projectors have limited resolution, making it difficult to see details in a map.

Most drawing and illustration programs used by cartographers provide WYSIWYG (what you see is what you get) functionality, and GIS programs have followed suit. This means you can see exactly what a map looks like before going through the time and expense of printing the map. GIS programs are also including color models such as CMYK, spot and Pantone colors to help ensure that colors in the final print come out as expected.

Map Goals in GIS

The goal of many in the GIS industry is to create a seamless, database-driven cartographic design processing system. After all, good cartography is based on good data. Many GIS developers, cartographers and national mapping agencies are also pushing for a digital cartographic model built around multiscale data. This approach will allow cartographers to create maps at different scales from the same basic database.

James L. Sipes is the founding principal of Sand County Studios in Seattle, Washington, and senior associate with EDAW in Atlanta, Georgia. Reach him at jsipes@sandcountystudios.com.