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.
(UMIACS-TR-2003-02)
(HCIL-TR-2002-26
