When I select any of the .OPS files, VASSAL does import the counters, but apparently not the map (i.e. in the module window there is a “pieces” button, but no “map” button).
However, when I choose to create a new game, then the map DOES show up!?
The game map is an image. You can edit the image with your preferred image
editor. (I’d recommend cropping away the huge, useless empty space at the
bottom.) The VASSAL module file produced when you save the imported module
in the Editor is a ZIP archive, so if you unzip it you’ll find the map image
in the archive’s images/ directory.
If you look under Help > Help, there’s a link in the resulting page to
the Reference Manual. It’s rather thin at present, and in many places is
out-of-date. One of our projects which will commence after VASSAL 3.1 is
released is to improve our documentation.
The map is just an image. Unlike ADC, VASSAL does not allow you to
create maps hex by hex. You normally have to scan your map or create
it in a graphics program. The importer has to draw the ADC map for
you and convert it to an image. You can edit the image in a graphics
editor if you open up the module (it’s a ZIP-file) and extract the map
(the map file’s name is similar to that of the original .MAP file, but
with a PNG extension instead).