The World Wide Web (www) has dramatically changed our way of producing, utilizing and consuming information, especially geospatial information in recent years. Web-based GIS (Geographic Information Systems) are designed to provide Web users analytical tools to assist their spatial decisions making process. With the advantages such as platform independence, customizability and cost effectiveness, Open Source Geospatial (OSGEO) software has been more adopted to develop Web-based GIS applications. Also, the increased availability of spatial functionalities in OSGEO software has opened many possibilities towards the implementation of a more powerful, interactive and collaborative Web-based GIS platform which is favorably referred to as the GeoWeb. However, compared with proprietary systems current open source based online GIS systems have several limitations. For example, most of them do not provide customizable web mapping service and spatial data processing service. However, these two types of services are essential to effectively filter spatial information and explore area of interest.
This research introduces a framework of implementing a Web-based GIS using Open Source Software, including Postgresql/PostGIS, MapServer, and OpenLayers. On the server side, Postgresql/PostGIS is used to store and process spatial data. MapServer is adopted to provide Web Mapping Service (WMS). Server side scripting language PHP is employed to dynamically generate map file from PostGIS for MapServer to render. On the client side, OpenLayers provides the programming interface to incorporate layers from different data sources into a same DOM container. Web-based GIS for political redistricting, as an example, has been developed to demonstrate both merits and demerits of adopting this framework.
Initial results of the demonstration show that the integration of PostGIS, MapServer and PHP could facilitate query based map generation and make mapping of massive spatial data efficient. Query based Web Mapping Service is capable to dynamically generate map and legend images. Spatial data handling functions in PostGIS are suitable for developing user interactive functions for querying, measuring and processing spatial data. Users could use the implemented Web-based political redistricting GIS to explore census, devise and evaluate new plan, and compare different plans. This framework based on open environment can be adapted to applications with similar requirements. The application implemented in this research can be access through gis.osu.edu/redistricting.