Roads and expressways in Chicago summarizes the main thoroughfares and the numbering system used in Chicago and its surrounding suburbs. Street layout Chicago's streets were laid out in a grid that grew from the city's original townsite plan platted by James Thompson. Streets following the Public Land Survey System section lines later became arterial streets in outlying sections. As new additions to the city were platted, city ordinance required them to be laid out with eight streets to the mile in one direction and 16 in the other direction. A scattering of diagonal streets, many of them originally Native American trails, also cross the city. Many additional diagonal streets were recommended in the Plan of Chicago, but only the extension of Ogden Avenue was ever constructed. In the 1950s and 1960s, a network of superhighways was built radiating from the city center. As the city grew and annexed adjacent towns, problems arose with duplicate street names and a confusing numbering system based on the Chicago River. On June 22, 1908, the city council adopted a system proposed by Edward P. Brennan; amended June 21, 1909. The changes were effective September 1, 1909 for most of the city. Addresses in Chicago and some suburbs are numbered outward from baselines at State Street, which runs north and south, and Madison Street, which runs east and west. A book was published in 1909 by The Chicago Directory Company indexing the old and new street numbers for most of Chicago. This volume is available online in PDF format indexed by initial letter, Plan of Re-Numbering, City of Chicago, August 1909. The opening text of the book says: EXPLANATORY The downtown area did not conform to this system until April 1, 1911, per an amendment to the law on June 20, 1910. Downtown was defined as Lake Michigan on the east, Roosevelt Road (Twelfth Street) on the south, and the Chicago River on the north and west. The addition to cover downtown was published, and is also on line as a pdf indexed by downtown street name. This additional paragraph explained the downtown changes: Chicago house numbers are generally assigned at the rate of 800 to a mile. The only exceptions are from Madison to 31st Street, just south of downtown. Roosevelt Road (previously Twelfth St) is one mile south of Madison with 1200 addresses to the mile, Cermak Road (previously 22nd Street) is two