Nope not at all. The lines weave in and out of zipcodes.
I have a buddy in another town, gets completely different RSN's and Locals then his neighbor who is 20 feet to the east in the same zip
Zip codes is one of the ways, but I believe they also use stuff like county lines, districts, etc.
In my home town of Rock Falls you are in a different DMA depending on if you live in Whiteside or Lee county. Whiteside county gets local channels from the Quad Cities on DirecTV, Lee county gets locals from Rockford. Houses literally across the street from each other get different local channels on DirecTV.
Comcast includes locals from both DMAs, so my parents get 2 ABC, 2CBS, 2 CW, 2 Fox, 2 NBC stations, etc.
Sometimes when I reflect back on all the beer I drink I feel ashamed. Then I look into the glass and think about the workers in the brewery and all of their hopes and dreams. If I didn’t drink this beer, they might be out of work and their dreams would be shattered. Then I say to myself, "It is better that I drink this beer and let their dreams come true than be selfish and worry about my liver."
-by Jack Handy