Most polling is done off zip codes and land line telephones. The move to cell phones represents an enormous problem for pollsters. Many people keep their phone and phone number when they move. This becomes a serious issue because now the pollster is getting inaccurate information about where the person being polled is actually going to vote and is registered to vote.
For example, me. I moved recently. Pollsters think I still live in Phoenix when I now live in Peoria. This is because my phone area code is 602 not 623 where Peoria is. They also think I'm voting in a different congressional race than the one I actually am voting in.
It can get worse. If you moved from out-of-state, you could well still have an area code that isn't even in the state you are in and the pollster wouldn't know that. Asking for a zip code doesn't help much since many overlap voting districts meaning there's no real way to know who you will be voting for for sure.
That's just a small portion of the problems brought on by new technology with polling and why so many polls tend to be inaccurate.