The Google Maps team have therefore decided to implement libraries for the API. A library is a set of Maps API features that are only loaded when explicitly requested by the application. This request is added to the call to load the API, e.g.,
The Geometry Library is the first library to be added to the Google Maps API V3. The geometry library provides a set of utility functions for performing distance, heading, and area calculations in a spherical geometry, such as on the surface of the Earth, and also provides functions for handling encoded polylines.
Ed Parsons has provided a good explanation of why and how you might want to use the Geometry Library in a post called 'Because the world is not flat...'. You can also examine the library in more detail in the Maps API Documentation and Reference.
Via: Google Geo Developers Blog