Multiscale Representation: A data generalization workflow and quality evalutation experience

In geographic data representation, users need specific tools for the representation and evaluation of the data on which the decision-making process relies. In cartographic applications, users need to deal with maps of the same geographic region at different levels of abstraction. In most cases one database per level of detail is maintained; a multiscale representation GIS would allow storage of all original geographic information in a single database and enforce the consistency of the different representations through appropriate, automatic generalization processes. In this paper we deal with the problem of geographic data generalization, beginning from a generalization workflow by improving specific routines. To reach the goals of the generalization process, we used the ESRI ArcGIS 8.1 platform. Inside this environment some generalization functions were implemented by improving appropriate routines in Visual Basic language. After a presentation of the generalization workflow, all geometric, topological and semantic cartographic constraints governing the generalization process are specified. In the next step these constraints will be translated into tools for assessing the need and the quality of generalization solutions. These tools are associated with a particular data model. For that data model the constraints can be best translated to measures and generalization algorithms and parameterized. This framework is based on constraints used to control the process and represent user requirements in such a way that the system is capable of reaching a quality close to these requirements; it reflects the idea that more than one acceptable solution to a given generalization problem may exist. The goal was the production of a topographic map at scales 1:50000, 1:100000 and 1:250000 from the “Carta Tecnica Regionale”, (CTR, official regional cartography) of the “Regione Autonoma della Sardegna”, RAS, (Regional Administration of Sardinia), at scale 1:10000, in a GIS environment. In accordance with official national and international standards, we provide the definition of the characteristics and associated quality evaluation tool to be used in validating geographic data