Some links to programs that convert vector data in other formats to the Garmin Polish Map (.mp) format; the data can then be imported into map editors like GPSMapEdit and MapMan for use either by themselves, or as part of more complex maps.
ezimg: Supposedly converts GPX and KML files to .mp format, and comes with an older version of the cgpsmapper compiler to directly generate .img binary Garmin map files. I say supposedly because I get an error message on my system, and no valid .mp or .img file is created. Others seem to have gotten it to work; may be a Windows 7 issue.
ocad2mp / ocad2img: Posted about this already, briefly. OCAD is a vector map drawing program, popular in Europe. ocad2mp converts an ocad file to Garmin .mp format, along with special formatting data to duplicate the exact look of the map on a Garmin GPS. ocad2img is a Perl front-end to ocad2mp that also sends the .mp file directly to the cgpsmapper compiler to create a binary .img map file. See this website for a comprehensive step-by-step description of the process.
OZItrk2MP: Converts an OziExplorer .PLT file to a .mp file. Available in the “Files” section of the Yahoo Map Authors group (registration required for access).
Perl scripts: Along with a bunch of other GPS and Garmin info at this site, there are a couple of Perl scripts that will convert GPX waypoint files and GPX track files into transparent .mp/.img files. Haven’t tried ‘em, don’t have any experience with Perl, and don’t really have any inclination to learn it, but be my guest. Requires that cgpsmapper be installed on your system.