1, turn off unnecessary layers.

2. Clean up redundant blocks, primitives and empty layers. The command is purge.

3. Back up the original picture and thin out a new picture with CASS software. The slimming method is as follows: a, clean up the dense elevation points and read the map accurately. The command is to screen the elevation points; B, change the distance of contour lines to reduce the number of contour lines. C, if the contour line in the figure is in a fitting state, so it takes up a lot of memory, use the PEDIT command, select the polyline or 2D polyline, and then select option D; Alternatively, after selecting all assembly lines, select No Assembly in the Attribute column.

The thinned CAD topographic map can meet the design needs, and the design layer can be attached to the original topographic map after completion.

4. If the planning and design can be carried out in sections, it is also a good idea to divide the diagram into several small diagrams. Remember to clean up invisible primitives, blocks, empty layers, etc. Save memory with PURGE command on segmented topographic map.