I've been messing around with this idea in the editor, not for DayZ, but for vanilla/ACE Arma 2 stuff. Basically my idea was to make a sort of Chernarus "Urban Sprawl" and expand existing cities and towns. From what I understand, it is very difficult if not impossible to modify the base terrain of BIS's Chernarus. You can add what you want but you can't remove any of the existing map statics IE Buildings or trees. You can execute a script to "knock down" the trees, but the fallen trees will still be visible in game. This created some challenges, since I couldn't get rid of barns in the middle of my planned residential or commercial areas and I couldn't get rid of trees to make room for a cul-de-sac. Another big problem is the hills and slopes in the game. If you look at the map, Cherogorsk and Electro are both MUCH flatter than the rural and wooded areas in the game. There are two ways to place buildings on the terrain. The default is for the building to follow the terrain, which if the slope is significant enough, you'll be in a house that's on a 45 degree angle. The other option is to map the building to be upright regardless of the terrain, which solves this problem for closed structures, but in enterable structures, you might get a nice layer of ground coming up through the floor (not too big of a deal in an apocalyptic setting. Still, I wasn't daunted. MBG's EU Buildings addons basically allow you to place any building or object (more than the editor's default limited selection). So far, I've been able to grow Chernogorsk at least 2-3 times its size by expanding the city in all directions and engulfing Prigorodki. Long story short, the idea to expand existing cities is possible, but to be able to find a clear and flat enough area to start a brand new city is a pretty difficult endeavor. The only clear enough places I can think of are the barren areas beyond the map border that some people spawn-bug into, but you'll have difficulty using a map in these areas.