Colour‐coded pixel‐based highly interactive Web mapping for georeferenced data exploration

Abstract

This paper describes a pixel-based technique that enables highly interactive Web choropleth maps for georeferenced data publishing and visual exploration. Instead of delivering geographic knowledge to the client in polygon-based vector formats, we encode geographic object IDs and shape information into highly compact pixel images (decoding maps). This allows the combination of raster and vector characteristics while avoiding the problems in the currently existing pixelbased (raster-image-based) or vector-based techniques. Differing from traditional pixel-based techniques that are static and allow very little user interaction, our pixel-based technique allows varieties of sub-second (less than 1 s) 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 with Web GIS techniques that use vector geographic data, our technique avoids transferring over the network large vector geographic data. It also avoids the non-trivial client-side computation to interpret the vector data and render the maps. Our technique features a short initial download time, near-constant performance scalability for larger numbers of geographic objects, and download-mapsegment-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 lightweight Java applets. YMap, an easy-to-use, user-task-oriented highly interactive mapping tool for visual georeferenced data exploration is implemented using this technique. The performance comparison of YMap to some other vector-based Web GIS demonstrates the feasibility and benefits of this technique.

The challenge of information visualization evaluation

“…We have demonstrated the feasibility of dynamic choropleth maps with a variety of platforms and network speeds [15], we are now exploring the challenge of providing access to the data for blind users [17]. Simultaneously, other dynamic choropleth maps are being developed and it is not clear which tool will become a standard for dissemination of statistical information data to the public.…”

“…Researchers work with high-end computers but they need to address the range of devices and network sp eeds available in people's homes and businesses. Special algorithms are needed to guarantee rapid downloads and adequate interaction [15]. Visually impaired users may need to use text -based alternatives to the visual display; an example is provided by the National Cancer Institutes cancer maps [2] which provides table views in addition to maps.…”

Integrating publicly available web mapping tools for cartographic visualization of community food insecurity: a prototype

“…In general, there are two approaches to web-based choropleth mapping: vector-data-based, client-side rendering and raster-data-based, server-side rendering (Zhao and Shneiderman, 2005;Schmidt and Dev 2008;Neutze 2009). With the first solution, a clientside application downloads vector geographic data from a server upon initial loading.…”

A Technical Solution to Allow Off-line Mobile Map Querying of Discrete and Continuous Geographic Attribute Data

“…Previous works (Andrienko and Andrienko, 1999;Dang et al, 2001) served as a foundation for Zhao and Shneiderman (2005) to design a methodology based on the coding of attributes within an image and associated with the pixel colour. The work of Zhao and Shneiderman is oriented towards the distribution, visualisation, consultation, and manipulation of choropleth maps using web applications.…”