Phoenix has interesting geography. I struggled to describe it, so I checked Wikipedia, which has this succinct description:

"Other than the mountains in and around the city, the topography of Phoenix is generally flat, allowing the city's main streets to run on a precise grid with wide, open-spaced roadways."

https://en.wikipedia.org/wiki/Phoenix,_Arizona#Geography

Possibly, the flat image might come from Arizona being flat where a large number of the people live, like Phoenix and its outskirts.

Grandparent's "damn near perfect grid" comment also jives with the layout of much of Phoenix.