This probably isn’t really the answer you’re looking for, but I don’t think it has as much to do with locations as, simply, the whims of the networks and the call of the lowest bidder–that is, whichever network will cost them the least to become an affiliate. (Or pay them the most? I can never remember who pays who in this scenario).
I was raised in Toledo, OH, and now live in Ann Arbor, MI, so I’ve dealt with the Toledo/Detroit market all my life. For many many years the lineup was thus:
2 (WJBK Detroit): CBS
4 (WDIV Detroit): NBC
7 (WXYZ Detroit): NBC
11 (WTOL Toledo): CBS
13 (WTVG Toledo): NBC
24 (WNWO Toledo): ABC
With the addition of FOX, we gained:
36 (WUPW Toledo): FOX
50 (WKBD Detroit): FOX
Then… came all of the changes, and they all happened in the space of two-three years, right around the time UPN and the WB started becoming, sort of, competition, and at the same time Disney was buying out ABC:
50 went from FOX to UPN.
2 went from CBS to FOX.
CBS was relegated, in Detroit, to UHF 62.
13 Toledo was bought by ABC/Disney. (They’re not an affiliate; they’re owned outright).
24 Toledo became NBC since NBC no longer had an affiliate in Toledo.
All of these happened within a very short time-span, and as I said at the beginning, it seems subject to whims more than to logic.
LL