That sounds like a realyl cool idea and I'd be more than up for that! Need to get more city map practice anyway!

The Guild World map last year worked out mostly okay with that similar sort of format and was great fun to be a part of! (...and see how many coconuts ChickPea was going to steal from my realm...probably hiding them somewhere in her sewer home... )

A time limit is a definite or else so much wouldn't get done. As for someone else filling in the unfinshed gaps, I guess you could have a more definite post-deadline deadline saying that those parts are liable to get redone which would either spur people on to finish their parts or allow new people to take part, or for those who have the time, people to do another section of the map, though perhaps in a different style to their first.