Most free GIS programs have a measuring tool that lets you determine the distance between two or more points. But this distance is usually a flat, straight-line distance, and doesn’t take into account the additional distance you would travel if the terrain weren’t flat. If the terrain is steep or hilly, your 3D distance traveled is longer than that flat, straight-line distance.
MicroDEM has the capability to determine both the straight-line distance and distance over terrain for an arbitrary path. After loading in a digital elevation model (DEM), click on the Distance (stream selection) in the window’s toolbar:
Then draw the path on your DEM:
And MicroDEM brings up a window with the flat distance, and 3D distance over terrain:
If you have a map whose area is covered by the DEM, you can draw the path directly on the map:
MicroDEM links the map with the DEM, and will calculate the straight-line and 3D distances: