Often, it reflects the age of the town. Grid layouts were very common from the mid-19th century to about World War II. For example, Boston's colonial-era city

Often, it reflects the age of the town. Grid layouts were very common from the mid-19th century to about World War II. For example, Boston's colonial-era city center is a mess, but Back Bay and Cambridgeport are an orderly grid, and the postwar suburbs outside Route 128 are sprawl. A city like Chicago did not exist in 1776, and so it has a more orderly downtown. There's also a certain path-dependence at work. Western states were also laid out in a rectangular grid by federal land surveys, and thus arterial roads often fell on the boundaries. Subdivisions, however, can be much messier, depending on when they were developed and what the developer felt like doing. Compare Seattle (prewar) to its outer suburbs across the lake (postwar). Or inner Phoenix (prewar) to outer Phoenix (postwar).