I can give you an example here in OH. The northern third is overwhelmingly Dem (give or take a precinct). The southern third is GOP. Columbus to Dayton is the battleground area. There are certain precincts in Dayton, where I live, that are battleground precincts-—when we see if Republicans are turning out you can pretty well predict they will go GOP (the exception was 2006-—but it worked in 2000 and 2004). If you poll those precincts, you don’t need to wait for either Cleveland or Cincy to come in-—they remain pretty constant. So by just tallying up the key precincts, you can usually count on the heavy Dem to go Dem and the heavy GOP to go GOP, and that will give you your number.
Thank you! That’s an excellent example and quite instructive.