[intertextuality]

They tend not to be grids because a lot of cities were built before the advent of cars, and renovating would be basically impossible.

Cities that had the opportunity to rebuild (like Chicago after the 1871 fire) make use of grids.

[greatpatton]

Grid structure is not dictated by cars. Roman cities were based on a grid structure.

[njarboe]

Lots of cars around in 1871. I think grids are useful layouts for cities that don't have any motorists. Most of these gridded cities were designed before cars. Modern suburbia loves the cul-de-sac.

[sgt101]

I was thinking of natural structures like the branches of trees and the tributaries of rivers. Because cities rebuilt like that in the 20th c does not mean that it was a good idea or successful.