In the early days of TV (which officially began in 1946) channels were assigned as stations requested them. Naturally the first TV stations were built in the biggest cities- NY, LA, etc. Well by 1951 the FCC realized that with only 12 VHF channels there was not going to be nearly enough to cover the whole country and people in smaller towns were going to be left out so they put a freeze on new licenses until a plan could be worked out to distributed the channels more equitably and fit the most stations in without interfering with each other. It was such a big project that no licenses at all were issued for two years which really pissed off a lot of people wanting to put stations on the air.
So in 1953 the FCC announced a "channel allocation system" based on the population of a city and what other cities were near-by. Naturally the big cities got a number of channels, while smaller cities got only one or two. In addition if their were groups of two or three smaller cities close together they were counted as one population area since the FCC figure people in one city could also see the stations in the neighboring towns.
Like in my case, I grew up in Greensboro, NC, a city of some 100,000 at the time (240K now). It was located 12 miles from High Point and 18 miles from Winston-Salem so the FCC considered the three as one population center and assigned one VHF channel to each town- Ch 2 for Greensboro, Ch 8 for high point and Ch 12 for Winston Salem which in theory gave the area all three major networks. In practice however not everyone could get a good picture from all three stations. For some reason we had a especially difficult time getting the ch-12 from Winston-Salem. Having a TV antenna on your roof was a status symbol and the bigger and higher it was the more impressive you were because it showed you could get more stations and clearer pictures.
The FCC also open the UHF band to augment the VHF band and smaller towns got only UHF channels. Broadcasters hated UHF channels because they didn't go as far and fewer people could see them so many UHF stations went bankrupt during this time.
By the 1960s cable-systems became commonplace which solved these reception problems and even brought in signals from distant towns so even small towns could get multiple channels. Today ofcourse, even someone located way out in the most remote boonies can get hundreds of channels crystal clear through DirecTV or Dish-TV satellites so everybody should have plenty of TV to see now. Pity there's nothing worth watching.