Abstract: According to the large amount of DEM data, in order to enhance the data readability and improve drawing efficiency, we optimized the traditional process of drawing the contour lines. The entire process was divided into three operations: Data preprocessing, building height index, mapping in accordance with the index. First of all, by collecting and simply processing the original DEM (digital elevation model) data, we extracted the key information related to mapping in the data, such as the latitude, longitude, maximum height and minimum height of the endpoints left-up and right-down in the whole map. Secondly, based on data preprocessing, we analyzed the data again through the equivalent point judging, the equivalent point linear interpolation and the equivalent point tracking to establish the strongly readable index files of height. At last, according to the height index data, the data structure was constructed to reasonably store data, so it could help the computer fast drawing contour map.

Key words: DEM, contour, linear interpolation, data structure