Well if Goldmap works for you you could use it.
Also I found pokemon GSC editors packed in a zip-file so you could check it out: http://www.sendspace.com/file/tqmb9i
Most of them didn't work for me so I just deleted them when I downloaded that myself.
"First you need to load Pokémon Gold or Silver rom from
File/Load... then select category of map and map then it
starts loading tileset what map uses. It needs to be done
only once. You can save from File/Save it will overwrite
file you opened or you can save into diffrent file from
What category of map? The only related option I see is Load Map. That part of the readme is not exactly helpful so how did you do this?