Quote Originally Posted by gazhekwe View Post
Woodward and John R are parallel until Six Mile, heading northwesterly, then John R straightens out and heads due north. Woodward continues on its northwesterly course. Keeping the divider at John R made sense geographically.
South of Six Mile, the Detroit street grid in the center of the city follows the old 18th and 19th Century directional pattern set downtown by the angle of the river. So all of the "northward" streets actually run NNW.

North of Six Mile though, in the "true" directional grid set by the Northwest Ordinance survey, and followed in the rest of the state [[and most of the U.S. west of the original colonies), asserts itself. So, as gazhekwe states above, while Woodward continues on its eccentric path, John R, along with most other north-south streets, straightens out to a true northerly course, and runs that way off into Oakland County, nearly all the way out to Rochester.

If you look at a map, and note the rest of the grid of major streets in Detroit north of Six Mile, it really only makes geographic sense that the east-west dividing line switches over to John R there. Especially since this part of Detroit is made up of former township land annexed into the city beginning in 1916, in which all of the lots had already been platted on a true north-south axis.