The DPLA currently geocodes items by looking up the text in the 'spatial' fields and running them through the Bing geocoding API - then uses geonames.org to pull state/country information based on the coordinates.
In some percentage of cases this doesn't work, and we get incorrect results from Bing, because the input data was imprecise, or misinterpreted.
It is hard to detect when this happens, other than by noticing items placed incorrectly when looking on the map.
Identify how many items are incorrectly geocoded (either by exhaustive search or sampling)
For ones that are wrong, find the right coordinates
Use Mechanical Turk to present people with map and geocoded items and have them flag bad ones
Create a game which uses the combination of map and location name to achieve the same goal