And as this prairie land in northeastern Illinois was developed into the city of Chicago, those main roads evolved into today's main streets, one mile apart. And most of the streets at the half mile intervals also emerged as rather important. And it is on these important streets where Chicago's street railways were developed, evolving into the present grid network of CTA bus routes.
In Chicago, there are 8 "standard" city blocks per mile. Although many blocks are further divided in half. A standard block has 100 address numbers, meaning there are 800 numbers per mile. Chicago address numbering begins downtown at State Street and Madison Street, State Street is 0 east and west, and Madison Street is 0 north and south. The major streets a mile apart have address numbers which are multiples of 800.
On Chicago's south side, the east-west streets are numbered. And those numbers correspond to the address numbers, in hundreds. For example, 87th Street is 8700 south. There actually were "errors" over the first 3 miles south of Madison Street, resulting in 12th Street, 22nd Street, and 31st Street being the first 3 "mile" streets south of Madison Street. South of 31st Street, there are 8 numbered streets per mile. 12th Street eventually became Roosevelt Road, while 22nd Street is now Cermak Road.
There are a few exceptions to this otherwise logical street numbering system. Most notably a 3 mile segment of Archer Avenue, a diagonal street on Chicago's southwest side. Many of Chicago's suburbs use the same numbering system as Chicago, while other suburbs use their own systems.