Why it looks like this

Chicago's grid is arithmetic: eight standard blocks to the mile, addresses counted from the corner of State and Madison, so any address tells you exactly how far you are from the centre. The fire of 1871 erased the young city's core, and it rebuilt fast on this system — the same flat, orderly network that let it invent the skyscraper.

The exceptions prove the rule: diagonals like Milwaukee, Clark and Archer Avenues slice across the grid because they are far older — Native American trails along ridges of dry ground, absorbed into the street plan.