Simple Method of Protracting Isoline in MapX

The paper introduces a simple algorithm of tracing isoline which is the same with the digital model ingrid format. And the algorithm can avoid the uncertaity of connecting and tracing the isoline. On the basis of the algorithm, we program the computer to protract the isoline in VC++ by using MapX control as a graphics tool, and accomplish the basic GIS function of magnifying, diminishing, roaming, and analyzing and querying the spatial data and attributive data.