I've loaded a bunch of the census data. We're looking at using it for both geocoding of addresses, and also for census fact lookups (by tract or block or whatever).

The issue that we've bumped into is in geo coordinate accuracy... depending on the service we use, we've seen the same text address return coordinates up to 10 miles apart. We have plans for addressing the quality of it all, but it raised an interesting question...

The question is, when the US census data is being collected, how is it associated to the shapes (block/tract/whatever)... do they have a GPS in-hand and log the coordinates onto the piece of paper, or do they just log the address... in the case of the latter, is it known what service or data source they use for geocoding the recorded address?