Research On Map Symbol In GIS

The fast development of modern technology, in which the computer technology is the most representative, has brought in inexhaustible power for cartography and GIS. The way from cartology to the combination of cartology and GIS is the natural law of scientific development. GIS is the development of cartology in the information era. GIS is the extension of the theory, method and function of cartology through the comparison of cartology and GIS. Cartology and GIS can be traced to the same origin, and are both the science of spatial information processing. Map is the primary source of GIS. GIS will be nothing without geographic data. So, plays on important role in GIS field. Map symbol is the language of map, and the basic mean showing map content. Map symbol can not only express the spatial location, shape, mass and amount character of an object, but also illustrate the inter-relationship between objects, and the general characteristic. The geo-spatial data is very complex, and the thesis and element types illustrated by map are numerous. Then it is necessary to set up an integrated map symbol managed by symbol database to illustrate various elements perfectly. Therefore, the map symbol database is an essential basic module in GIS, and has been developing with the development of IT as the basic research subject of GIS. To design a comprehensive, systematic and precise symbol database in GIS is significant to the application of GIS.Theory is the forerunner of technology, it's blindfold technique without the technology supervised by advanced theory, and it's also behindhand theory without the theory sustained by advanced technology. To comprehended and mastered the basic theory of map symbol is the prerequisite of developing symbol in GIS successfully. The paper presents a comprehensive summarization of map symbol theory, from the concept, category, characteristic, function, vision variable and vision effect of map symbol, which is the key to the research and the development of map symbol in GIS.There have difference subsist in 2D map symbolic expression and 3Dmap symbolic expression.2D symbol give expression to geographic element by a kind of abstract mode, and the user spell over symbol on map should have some certain trainings sometimes, whereas 3D symbol is better than 2D symbol on readability, It gives user third dimension and make the symbol more visualization, also can supply prolific information, So user can comprehend the signification of map symbol without training. With the development of computer technology in recent years, it have became fact which depict realistic spatial information by 3D symbol. Although 2D symbol still apply widely for the moment, but the appearance of 3D symbol have brought in huge challenge for 2D symbol revolution. The paper summarizes and studies the 2D symbols and 3D symbols in the GIS map symbol, on the basis of the development of GIS from 2D to 3D.On the research of the 2D symbol in GIS, the symbols are categorized as point symbol, line symbol and fill symbol. Firstly, the point symbol is analyzed and studied, and then the point symbol database is designed and implemented based on the characteristic of point symbol, the theory and analysis of picture composition. Secondly, three drawing methods of line symbol are introduced, i.e. pure function method, transverse cycle and lengthways pile. Based on these methods, the line symbol database is designed and implemented. Finally, fill symbol database is designed and implemented after the analysis of characteristic and picture composition of fill symbol, and the descriptions of three fill methods of fill symbol. The effect of illustrating related symbols from the symbol database in the vector map is very nice. The symbol database in the paper is implemented based on object-oriented technology and Visual C++6.0 platform, with friendly interface, convenient operation.On the research of 3D symbol of GIS, a summarization of the 3D symbol is given first, followed by introduction of the developing situation of 3D symbol. At present, ArcGIS 9 is unique in the research and practical application of 3D symbol. Because of the critical limitation in the presentation of spatial information with 2D map symbol, 3DGIS is receiving more and more attention, so the research of 3D symbol is very necessary. Referring to the category of 2D symbol, the 3D symbol is divided into four categories, i.e. 3D point symbol, 3D line symbol, 3D fill symbol and 3D solid symbol, meanwhile the illustration of composition elements and depth elements of 3D symbol is analyzed. The 3D fill symbol, i.e. the 3D terrain, is implemented by using OpenGL in the end of the paper.Finally, the summarization and prospects of the research in the paper arepresented.