Inkscape

Inkscape is a free, open source drawing program. The advantages of Inkscape for a cave cartographer are many. First, it is free. Second, it has many of the features of Adobe Illustrator. Third, the internet is full of tutorials on how to use it. Fourth, it is open source. This means that any enterprising caver with some programming skills could add features specifically adapted to cave cartography.

This does not necessarily mean that everyone should be using Inkscape. One big disadvantage of Inkscape is that it can be very slow on larger cave files. Anything over about a mile is probably best handled in Illustrator. Since Inkscape is constantly being improved, newer versions may solve the speed problem. Comparing Drawing ProgramsClick here for a more detailed comparison of Inkscape and Adobe Illustrator.

In addition to Inkscape and Illustrator, other programs such as Corel may work just as well or better. In fact, as SVG becomes supported by more and more drawing programs, the options for cavers will only increase.

Compass Support. Since  drawing programs can be very expensive, Compass was specifically written to be sure it would be compatible with Inkscape. There are extensive tutorials on generating cave maps using Inkscape on the Compass web siteand in the help files for the "Sketch Map Editor.

You can download a copy and get more information on it here: http://www.inkscape.org/

I would advise that you try to get a copy of version 2.7 or better. Older versions have bugs that cause problems copying and pasting drawings between layers, which is something will need to do for creating masks.