Beyond Road Maps: The Topography of Digital Mapping Databases
Mattison, David, Searcher
"A map is not the territory it represents, but if correct, it has a similar structure to the territory, which accounts for its usefulness."
--Alfred Korzybski (1879-1950), Science and Sanity (4th ed., 1958).
Ever since I joined the Boy Scouts, I've been fascinated by maps. Cartography, or mapmaking, is an exact science as well as an art in design and presentation. Going beyond the science and accuracy of the map, cartography also involves cultural, political, and social values, e.g., biases, not just of the Western mind, but of anyone who marks their territory with a line in the sand, a mark on a cave wall, or in binary digits. As Stephen S. Hall eloquently put it in the conclusion to his book, Mapping the Next Millennium (1992), "We must see not only the information they purvey, but the biases they may conceal, the ideologies they may preserve, and the abuses they may invite." For the present, however, I will confine this survey to digital maps and their databases.
Maps are like the Internet, a communications medium and simulacrum of the world sometimes requiring expert knowledge, or, at the very least, a basic knowledge of how to navigate across and through manifold layers of information. The many cultural, political, and social issues surrounding the Internet, problems such as the "digital divide," copyright, and even basic computer literacy skills, apply equally to Web-based maps. Webmapping services are an increasingly powerful new information commodity and resource, leading to a growing need for "map-literacy."
Not counting nonspecialist individual map users, the Web mapping and geographic information systems (GIS)/ spatial data world is roughly divided into four parts:
* The academic, where students learn how to operate a GIS (Geographic Information System) or how to use GIS and other spatial data visualization products as research tools.
* The commercial, where spatial data and visualization applications and data are developed for business (profit) reasons and distributed.
* The government, some of whose activities mirror and supplement the commercial, including data acquisition, along with the creation and maintenance of standards and software.
* The non-commercial, including activist and community organizations which can now generate their own maps.
Most of my examples come from the first three areas. In this article the term GIS is used synonymously for spatial data applications and visualization tools that may not have a geographic component, but which use the GIS model of user-selectable data layers, scalability, and data queries.
Web maps, like other kinds of computer graphics (still images), fall into two categories: raster (bit-mapped or pixel-based graphics) and vector (lined-based graphics). You can always distinguish a raster from a vector graphic by the quality of visual data: A raster image will pixelate at the highest and beyond resolution or level of magnification. Typically, in a vector-based map, this kind of overzooming, depending on the number and density of data layers you select, produces what appears as a blank screen. The file formats for each of these categories include common raster formats, such as GIF, JPG, PNG, and TIF, and many specialized and proprietary vector formats developed by digital mapping application vendors, government, and research agencies. The Scalable Vector Graphics (SVG) specification, since it belongs to the XML vocabulary, may offer some relief from competing vector authoring and display formats. To follow the fast-moving SVG area, consult the W3C overview site on SVG [http:// www.w3.org/Graphics/SVG/Overview.htm8]. GIS authoring and viewing applications integrate these raster and vector graphics. On the GIS authoring side, vector maps, such as electronic navigational charts, are often produced from raster maps by a line-tracing software process. On the viewing side, raster graphics, usually remote-sensing images, may be included as a data layer to provide a more realistic two-dimensional visualization experience. …