I'm not sure if Clint Eastwood's character "The Man With No Name" (Blondie) wore a serape or a poncho. From some angles it's wrapped like a serape would be, but from others it looks like there was a hole in the center and it was worn like a poncho.

https://www.youtube.com/watch?v=M-k_BW8iLkk

The thing I've always wondered about ponchos is how they shape them. Unlike serapes they're usually not squares, so how does the weaver know exactly where to stop weaving to get the right shape? Or are they just cut from a square and then have the edges tied of?

It's a poncho. As your clip shows, he sometimes throws the front part over his shoulder which makes it look more like a serape.

Why is every commenter calling sarapes "serapes"?

Edit: TIL "serape" is used a lot in English. It caught me off-guard because I can't imagine why isn't the original word used.