system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How are there national radio stations but local ads?

I've found that when I'm driving round there'll be a national radio station with the same presenters and songs etc, yet all the ads are for local businesses. How do they time all the local ads around the country to end exactly on time when the national presenters come back on air?
gpt
National radio stations' content has to be rebroadcast by local stations. Local stations sell advertising and just broadcast that during commercial breaks the national broadcast contains.

It's similar to how you can watch Jeopardy (a national broadcast program) and still see an ad for a local restaurant.