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Some Map Basics

Computer mapping has evolved around the convergence of three technologies: vector drawing, raster images, and databases. SVG directly addresses vector and raster capabilities, but until future standards like XML Query are widely implemented, additional non-XML tools are needed to provide database access. There are several approaches to database access, all requiring some type of server technology for database linkage. CGI, ASP, and PHP can all be used in this capacity. However, this case study will focus on Java solutions, which are portable to a wide spectrum of servers, as well as being highly extensible with an apparently unending stream of APIs.

There are some issues to keep in mind when dealing with maps. First, the amount of map data can be overwhelming. Even though vectors describe lines much more efficiently than raster images, terrestrial features will easily outpace existing bandwidth. Cartographers have developed several approaches to this problem, generally implementing some form of “divide and conquer” to split a map project into many smaller files. A regular tile grid and a hierarchical approach are two common methods of reducing the world to manageable chunks. This case study uses the hierarchical approach to present map data in successive levels of detail, as illustrated in Figure 25.1.


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