Journal of Geospatial Engineering, Vol. 4, No. 2 (December 2002), pp.111-123. Copyright  The Hong Kong Institution of Engineering Surveyors A Mapping Function for Variable-Scale Maps in Small-Display Cartography Lars HARRIE 1 , L. Tiina SARJAKOSKI 2 and Lassi LEHTO 2 1 National Land Survey of Sweden, SE-801 82 Gävle, Sweden - lars.harrie@lantm.lth.se 2 Finnish Geodetic Institute, P.O. Box 15, FIN-02431 Masala, Finland tiina.sarjakoski@fgi.fi, - lassi.lehto@fgi.fi Abstract: The aim of this paper is to examine the variable-scale method of presenting geodata for personal navigation using small-display mobile devices. Ideally, the user should have a large-scale map of his immediate vicinity for choosing the right direction at an intersection, for example. At the same time, the user requires a small-scale overview map where he can see his destination. A solution that meets these requirements is a variable-scale map, which is constantly updated to keep the user’s position in the large-scale area at the centre of the map. In this paper, a variable-scale mapping function is derived in accordance with some specific properties; then characteristics of the mapping function are visualised. Furthermore, real-time generalisation methods are used to adapt the original cartographic data to the small-scale areas of the variable-scale map. A prototype system of a variable-scale approach was created using the emerging XML-based vector-data standards (GML and SVG), where the generalisation and scale-variations were performed in an XSLT transformation. The prototype implementation of variable maps was tested in a case study. Finally, the potential and the limitations of variable-scale maps for personal navigation using mobile devices are discussed. 1 Introduction In the near future an increasing number of maps will be displayed on portable computers and mobile telephones. These maps are often referred to as mobile maps. A major problem with mobile maps is their small displays, which put high demands on the selection of cartographic data to be shown. This becomes problematic when the user requires a considerable amount of cartographic information. In personal navigation, for example, users often need both a detailed map of the area surrounding the current position as well as an overview map. This means, in cartographic terms, that the user requires both large-scale and small-scale cartographic data. This paper concentrates on a method of giving the user both large-scale and small-scale map information simultaneously on a small portable display. The paper is based on the previous paper by the authors (Harrie, et al., 2002). In principal, there are, three approaches to providing the user with both large-scale and small-scale maps on a single display: 1) The user switches between a small-scale map and a large-scale map. Advantage: Full view of both the small-scale and large-scale maps. Disadvantage: The user does not see the two maps simultaneously; and might therefore have difficulty connecting the information from the two maps. Furthermore, switching between maps is necessary. 2) The large-scale map is shown in the ordinary map window and the small-scale map is shown in a key-map. Advantage: The two maps are visible simultaneously. Disadvantage: Even though the user sees both maps at the same time, identifying common objects in the maps is often problematic. In addition, the key-map hides data in the ordinary map window, and it is often difficult to have sufficient space for both maps at the same time on a small display.