Here is an example layout made with the Sci-Fi city tiles from Gamecraft Miniatures.  These tiles are pretty neat and you can easily build a very modular and versatile city layout. 

I have a bunch of Gamecraft’s other products, naming the the 15mm modular structures for humans (since I’m a huge 15mm fan) and it’s all good stuff.

If you want the stencil for omnigraffle you can pick it up free on graffletopia here https://www.graffletopia.com/stencils/1230