All the the Plymouth and Dodge dealers in Metro Detroit in 1939 - according to someone. I will take this as a fact .. i recognize all these cities/streets.
If you were to drawn a semi circle, with downtown Detroit by the Detroit River as southern border (Journey didn't quite get it right in their lyrics .."south Detroit" is "Windsor Canada"

), the radius would be 30 miles to get all the listed cities on the map.
60% of these dealers however, were within about 15 miles, so mostly in Detroit city limits (dark yellow on the map, and where that color stops to the north is 8 Mile road) and 40% in adjacent suburbs or nearby cities.
aside - Detroit proper (not including suburbs) has more square miles (119 roughly) than Manhattan Island, San Francisco, and Boston combined. It once had population of 2 Million people too. 700,000 now. hence the blight issues it faces -- but perhaps I will take that to the Urban Sprawl thread with the politics left out
Looks like I have a winter project -- unfortunately I can already tell its gonna be a bit depressing - there are some rough Detroit neighborhoods NOW where many of these places WERE. But the buildings may still be there, however, the dealers are LONG gone.
The outlying areas - Romeo, Trenton, River Rouge, Mt. Clemens, Wyandotte, Ferndale, and Royal Oak - have a higher likelihood of standing buildings with businesses still in them.