If your playing over LAN then there is no bandwidth issues so make any kind of map using any kind of image editor with a variety of image tokens for the bits which might move. If your playing over a wider area network like an internet connection then it might be prudent to either a) make it with tiles like jfraz said or make the map bases downloadable before the games start and trust your players not to look at them before hand. If you cant trust them then just encrypt the files with something dead simple like bcrypt and hand out the passwords at play time and decrypt some of the bigger files "just in time".