Improving Automated Generalisation for On-Demand Web Mapping by Multiscale Databases
This paper describes the generation of maps on-demand with the use of a multiscale database. It is based on an analysis of the requirements of on-demand mapping and points out the different requests and limits of on-demand cartography. The central idea is
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Abstract This paper describes the generation of maps on-demand with the use of a multiscale database. It is based on an analysis of the requirements of on-demand mapping and points out the different requests and limits of on-demand cartography. The central idea is to combine two commonly used approaches in cartography: On the one hand the use of a multi-scale database which includes two or more levels of details, on the other hand the use of cartographic generalisation methods. For selected object classes the paper discusses and evaluates design and implementation options for the multi-scale database and the generalisation of parts of the framework. The importance lies in the optimal combination of these two methods – which tasks must be solved by the MSDB and which through the generalisation process. Keywords: multi-scale database (MSDB), on-the-fly generalisation, level of detail (LoD), web mapping, on-demand mapping
1 Introduction In recent years, a new field of application has opened for cartography: web mapping (Peterson 1999). More and more websites offer maps of various kinds (topographic maps, thematic maps) and topics (route planning, city guides, among many others.) over the net. Many of these websites are equipped with zooming capabilities, but as these are not true generalisation capabilities, the quality of most web maps is poor.
D. E. Richardson et al. (eds.), Advances in Spatial Data Handling © Springer-Verlag Berlin Heidelberg 2002
516 Alessandro Cecconi, Robert Weibel and Mathieu Barrault
1.1 Maps on the Internet Maps created for the Internet are based on different conditions than paper maps. The map provider cannot control many technical constraints and requirements. With respect to visualisation, several parameters cannot be defined, such as hardware (display resolution), system software (operating system) or application software (browser). Since the bandwidth is typically still narrow, it is also very important to take into account the amount of transmitted data in distributed systems. Despite technical restrictions it’s possible to create maps for the web, witness the numerous examples such as route planning, location finders and others (www.mapquest.com, www.map24.com). In functional terms most of those services, however, are not flexible as they have been designed for a well-defined purpose, such as providing locator maps for user-specified street addresses. Hence, the user has no opportunity to change anything or to define his/her purposes and requirements for the map graphics. To remedy these drawbacks a new strategy must be found which allows more flexibility for web mapping. 1.2 On-demand Mapping On-demand mapping is concerned with the generation of maps based on user request and according to user requirements. Users are able to produce their own maps and customise the process of generation. A short explanation of on-demand mapping can be found on http://www.ngdc.noaa.gov/seg/tools/gis/ondemand.shtml. It deals with the dynamic creation of digital cartographic products, like topograph
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