HCIL-2002-26

Zhao, H., Shneiderman, B.
December 2002
International Journal of Georgraphical Information Science, 19, 4, 2005.
HCIL-2002-26, CS-TR-4431, UMIACS-TR-2003-02, ISR-TR-2005-35
This paper describes an image-based technique that enables highly interactive Web choropleth maps for geo-referenced data publishing and visual exploration. Geographic knowledge is encoded into raster images and delivered to the client, instead of in vector formats. Differing from traditional raster-image-based approaches that are static and allow very little user interaction, it allows varieties of sub-second fine-grained interface controls such as dynamic query, dynamic classification, geographic object data identification, user setting adjusting, as well as turning on/off layers, panning and zooming, with no or minimum server support. Compared to Web GIS approaches that are based on vector geographic data, this technique has the features of short initial download time, near-constant performance scalability for larger numbers of geographic objects, and download-map-segment-only-when-necessary which potentially reduces the overall data transfer over the network. As a result, it accommodates general public users with slow modem network connections and low-end machines, as well as users with fast T-1 connections and fast machines. The client-side (browser) is implemented as light-weight Java applets. YMap, an easy-to-use, user-task-oriented highly interactive mapping tool prototype for visual geo-referenced data exploration is implemented using this technique. Keywords: Web GIS, choropleth map, information visualization, dynamic query, universal usability Web supplement: http://www.cs.umd.edu/hcil/census/YMap122002/smap.html
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