From ArborWiki

As with many flatland cities, Ann Arbor's Downtown is pretty much in the geographical center of the city, and contains the major civic and economic focuses of the city.

In Ann Arbor, "Downtown" may include areas as far away as the Kerrytown, State Street, and South University areas, or it may just refer to the 20-block area bounded roughly by William Street, First Street (where it borders the Old West Side), Ann or Catherine Street (where it somewhat merges into the Kerrytown area and Old Fourth Ward), and Division Street (where it borders, or merges into, the State Street Area).