For countries that either don't have postal codes, or postal codes are so new that people still aren't used to using them, the "human" name to lineup list will be available using the /transmitters/ API call. It's an option if your grabber wants to implement it as an alternate means of selecting a lineup.
What's your country: GBR
Do you want to select your transmitter list based on postal code or transmitter name? (postal code)
Present list of lineups.
Did you find your transmitter? Do you want to see the master list?
Since it's only done once during the setup phase, it's a little "wordy", but once done, it's done.
To your other thoughts:
Generating a bottom up map is time consuming; are "you" willing to pay more than $25 year?
I don't think adding all 60 transmitters to every request for lineups in a postal code makes sense, because it will just add confusion.
I believe the existing call for /transmitters/GBR already meets your suggestion of a region that has a list of all Freeview transmitters.
The mapping of zip codes to lineups in the US is probably 99% accurate, so nothing to be gained there.
If you're saying that there should be an additional call, like https://json.schedulesdirect.org/201412 ... e=freeviewhttps://json.schedulesdirect.org/201412 ... de=freesat
then that's more within the realm of possibility.