Abstract: We introduce our practical system that is applicable to very large topographic map. We present a practical algorithm for contour line interpolation, which can get rid of some fatal defects often found in the grid and triangular net approaches, known as "the interpolated line's intersection with mother contour lines". We propose an algorithm for contour line elevation interpretation. A practical algorithm for threedimensional regular data field is presented to handle a very large map, and the quality of the calculated grid elevation is high due to the sufficient exploitation of prior knowledge. The run-time complexity of the approach for establishing the 3-D regular data field is O(m+n), linear to the number of data points(m) and the number of grid points(n), therefore, the processing speed is very high. Finally, a real-time graph is created with the three-dimensional regular data field.