AN OBJECT-ORIENTED MODEL OF ELECTRONIC MAP DESIGNING:A STUDY ON THE SOFTWARE FOR THE NATIONAL ECONOMIC ATLAS OF CHINA (ELECTRONIC VERSION)
Chu Shiqiang; Liu Yue(Institute of Geography, Chins Academy Of Sciences and the State Planning Commision of P. R. China, Beijing 100101)
With the development of computer-aided cartography (CAC) incorporating geographic information system (GIS), electronic mapping system has taken on a new look with rich interactive and analytical abilities. This paper presents an object-oriented model for electronic map designing, and describes its implementing techniques systematically.On the basis of a thorough analysis of a number of cartographic works, such as the National Economic Atlas of China, adopting the object-oriented method, the author provides a conceptual model of electronic maps by abstracting two classes: "map class" and "map layer class" (Fig. 1).Each map has a main topic (usually described with the map name), and this topic may be divided into several sub-topics (themes) including a base map and thematic contents. Each theme is represented by a certain symbolization method with a specific legend, which can be taken as a kind of object "layer". Thus. a map can be considered as an organic entity, named "map object', which consists of the map name, the mathematical basis, map layers and the relationships among them.The map class should include a series of function members for map designing, editing. querying and analyzing, thematic data and figure output, etc. And thus, a conceptual model of electronic map can be deduced.Going a step further, the author summarizes a numbers of thematic map symbolization methods for economic and social phenomena, and establishes a library of computerized models of thematic symbols, such as "pie" graph, "bar" graph, "percent proportion table" graph, "population pyramid" graph. Based on those above, the author creates a model for electronic map designing, and sets up a series of mapping "templates". With these templates, map features can be visualized automatically with cartographers' own styles. In addition, a group of essential software resources invoked in mapping templates, such as the map symbol library. the map color library, the method library for cartographic index classification, the symbol-scale building tool, the data capture dynamic linking library (DLL) and the object linking and embedding (OLE) tool, are introduced.Developed in accordance with the strategy mentioned above, the software package MapMagic can produce multimedia electronic maps efficiently and has been successfully used in editing and compiling the Electronic Version National Economic Atlas of China. Through practice, it has been proved that MapMagic, as a thematic mapping software for general purposes, is a qualified method of editing compiling a variety of electronic maps on social, economic, or natural phenomena.