From what I understand, there isn't much to learn.
I recently(AKA today) played your GTA map abit, great stuff, but I don't really like the OMGOMGOMGOMOMGWINDOWSWINDOWSWINDOWS look, because, like when you think about it, imagine being in the building. Not every single building in a city will have windows for outter walls, so I'm trying to avoid doing that with all of the buildings.
Plus I like having not a million huge tall buildings, but rather a bunch of small ones and a few tall ones. The terrain I'm making isn't a huge famous city like New York City or L.A. or something, it's just a small one I've made up.
Plus, if I DO make this into a map, if it's okay with the creator, I plan on possibly making it a tribute to a mod for Unreal Tournament 2004(Killing Floor, if you wanna look it up), so this map would take place weeks after the total chaos, so everything would be in ruin.
And if you don't mind me asking, what kind of 'dead city' are you making? Abandonded or destroyed?
Edit:
Oh yeah, I noticed you're using the 3 stripes one way and two stripes another... I'm sure you know this, but why not just use the triple stripes from one of the brides?