Neat bit on Infamous world creation: http://www.gamasutra.com/view/news/27638/GDC_Infamous_Open_World_Trickery.php
The entire city in Infamous is made up of hexes where Sucker Punch's artists would place roads, buildings and other environmental pieces. Roads meet perpendicularly at the center of a hex's side, which allows artists to rotate hexes to create different configurations, as roads would line up from piece to piece. This meant less work for artists, but there is still good variation in the environment thanks to different hex configurations.
Another trick Fox and his team implemented was restricting player sightlines. By doing this, buildings and other obstructions hide the geographical limitations of a world. In Infamous, all of the street intersections are "Y" shaped -- this is a natural effect of the hex-based layout, but it also means players can't look straight down a long street. "If we provide really long sightlines, you get bored running down the street," Fox said.