What is the Calais API?
From the documentation:
The Calais Web Service allows you to automatically annotate your content with rich semantic metadata, including entities such as people and companies and events and facts such as acquisitions and management changes.
Version 3.1, currently in beta, has added information regarding the latitude/longitude of a few types of entities: Cities, provinces/states and countries. It makes it possible to plot those entities on a map, in a way similar to what can be done with the Metacarta GeoTagger API.