I have an idea for a mod I'd like to do that would require an original map.  I tried starting one in the cartographer's table, I made a large blank map so I could start from scratch.  It looked like it was all water, which was fine, but I couldn't figure out how to start adding land to it.  I tried selecting some different tiles, but no matter what buttons I pressed I couldn't get anything to come up on the grid.  Not sure what I'm doing wrong, or if its something with the program.  Is there any documentation on map making yet?