How can survey estimates of small areas be improved by leveraging social-media data?

At first glance, social-media data look like the antithesis of survey data - never to be used in the same sentence! By social-media data, we mean the sort of information one gets from Google, Facebook, Twitter, and so forth, about what "the crowd" is talking about or looking for. Exactly which crowd we are referring to is an important part of the science of crowd-sourcing.