The Drupal Placemaker utilises Yahoo!'s Placemaker API to provide geo-enrichment functionality for your content.
Geo-enrichment?
There's a rich vein of location data buried within your content. You're sure to find references to towns, cities, regions and countries scattered about your node's body fields. The Placemaker module acts as a bridge between your content and Yahoo! Placemaker to parse, extract and index references to the location information within your unstructured data.
Why?
Once your content has been geo-enriched, with help from Yahoo!'s Geoplanet API and a faceted search engine such as Apache Solr, we can use spatial relationships in a similar way to Drupal's taxonomies to group content on the basis of the geographical relationships identified within content.