Ok first of all, I love this idea.
One thing I would like to point out is that a city can be interpreted in a lot of different ways, but I'm pretty sure all you guys are talking a "modern city" type thing with like, cars and stuff. (words like "roads" in Benlin's comment, or "Main Street" in Mike's give me that impression at least) If anyone has any other different types of cities they want to propose, they should probably speak up now.
Oke so me and Snow talked and we figured that the best location we could find was this island right here:
The island isn't too big. It's not too small. and the terrain is actually quite nice, if you can imagine grass instead of ugly mycelium.
Anyway this is why I said we have to decide now if we're going to do modern or not: While the terrain will look quite cool if we give it a grass makeover, depending on the type of modern city we do, we will definitely have to level it, and that's just no fun, nor is it a great way to start a community project. The claim is about 400x400 to give you some context. Be sure to let us know if you think we should flatten it or not
Edit: or we could partially level it and only remove all the hills. That's probably where I put my vote, personally - but it's not just for me to decide so be sure to comment if you want to be a part of it!