hey Ben,

The image you are working from is 3d!

you could try switching to mental ray, and use physical sun and sky under the enviroment options at the bottom of the mental ray render options. if you do this you should dsable default lighting. (this is near the bottom of the common render settings),

...but before all that, do you have a bump map on the model? and have you beveled the edges of the buildings? they look kinda sharp. (maybe thats just the anti-aliasing)