[smirt362]

Downtown areas are almost always organized in a grid pattern with 90 degree angled streets...as it extends out and gets more sub-urban you see more of a variance in the angle and direction of streets...but mostly people like to use 90 degrees because it's organized and it helps define a "block." I would create/design the terrain first and the build the city on top of it...that would give it more of a natural feel.