Institute of Cartography, ETH Zurich
ETH Hoenggerberg, CH-8093 Zurich
keywords: interactive vector-based topographic maps, open-source technology, SVG, spatial databases, PostgreSQL, PostGIS
Publishing larger geographic datasets on the web often required expensive GIS or commercial database software in the past. While many commercial systems had been able to handle large databases for some time, file-formats delivered to the client were either standard-based and non-interactive (e.g. raster-based tiles) or highly proprietary, but would allow for interactivity. Most commercial systems that allow client-side interactivity, base their clients on proprietary platform-dependent plug-ins or Java-Applets, which often include the use of proprietary and undocumented data formats. Additionally, many commercial products lack (carto)graphical quality and have severe limitations when it comes to interactivity and flexibility. With the introduction and continuous development of the SVG specification and SVG conformant tools and viewer, cartographers are for the first time able to publish high-quality cartographic data, based on an open and vendor-neutral standard.
Delivering larger geographic datasets requires that a map server is able to extract subsets of existing data. This paper describes a client-server solution using PostGIS, an open-source extension to the free SQL database PostgreSQL. PostGIS is an OpenGIS conform spatial database and uses the OpenGIS Simple Features Specification for SQL (e.g. Multipolygons, multilinestrings, etc.). Apart from spatial queries, PostGIS, in collaboration with the "proj4 libraries", can project geographic data on the fly, can calculate distances and do simple analysis. Serverside PHP scripts take care of the communication with the spatial database, database queries, calculations, simple analysis and formatting of the resulting data, prior to being sent to the map client. The presented spatial database holds various scale levels of the vector datasets provided by the Swiss Federal Office of Topography. Depending on the scale and extent requested by the map client, the server can deliver different datasets and symbolize the data appropriate to the map's scale.
The presentation includes a demonstration of a new version of the topographic map client, as already presented at SVG Open 2002 in Zurich. Additions and improvements of the map-client include extensions to the interactive profiling tool, improved map navigation, a NMEA 2.0 compatible GPS data display as well as an animation of hiking routes selected by the map user. The map client can communicate with the map server in order to load additional map data when zooming and panning. The Adobe extensions ".getURL()", ".postURL()" and ".parseXML()" take care of the communication. The requested data can later be added to the existing map's document object model without having to reload the web application.
Aside from a prototype of a nation-wide interactive topographic map, based on data provided by the Swiss Federal Institute of Topography, an additional SVG based Online-GIS application, operational in a Zurich based geology consulting company, will be presented. This webapplication allows to disseminate and visualize spatial data in the domains of geology, hydrology and hydrogeology, used internally within the company, and allows to find locations of the company's consulting reports, accumulated during the last 40 years.
The result of the current work illustrates that it is possible to implement webmapping systems based solely on open-source software, that are not only significantly more cost-effective than many commercial systems but also feature higher graphical quality, interactivity and flexibility.