Maps Alive: Viewing Geospatial Information on the WWW

Abstract We describe a WWW-based system — consisting of browsers, servers and connecting protocols — which allows users to view, search and post geographically-indexed information of the Earth. Much information available on the WWW, such as weather reports, home pages of National Parks, VRML models of cities, home pages of Holiday Inn hotels, Yellow and White Page directory listings or traffic and news reports, is better located and visualized when displayed directly or via clickable anchors on top of 2D maps or in full 3D environments. We have developed two geographical browsers: a 2D map browser capable of continuous scroll and zoom of an arbitrarily large sheet and a 3D flight-simulator browser capable of continuous flight around the Earth. Both browsers download and cache geographical information, geometrical models, and URL anchors in small regions called tiles. The tile caching process is based on the user's current position, velocity, and acceleration in the 2D 3D space as well as on the latency of server replies. A user can program these browsers by adding small application programs — mapplets. On the server side, we have developed geographical and geometrical servers which contain very large data bases of images, elevations, lines, points and polygons stored in tiles structured into hierarchical pyramids or quadtrees. We have also developed a metadata server which contains, in hierarchical layers, URL pointers and geographical coordinates of various WWW documents, geographical information and geometrical models.