The US Patent and Trademark Office has granted two patents to Google, one for 'methods and apparatus of estimating similarity' and one for a 'digital mapping system'. 

Patent number 7,158,961 concerning the 'similarity engine' was initially filed in 2001 and has taken over five years to receive approval.

It describes a method whereby a similarity engine generates compact representations of objects called 'sketches'. These sketches, which contain weighting according to placement vectors, can then be compared for similarities.

The significance for Google is that such an apparatus could greatly improve search results by allowing its spiders to distinguish between duplicated information on web pages, and thereby streamline searches.

Many patents have been filed for similarity methods and devices in recent years, including a couple from IBM and Hitachi. 

Searching Google's own Patent Search database for 'similarity engine' returns 15 results issued in the past decade alone, including two 'similarity engines for content' patents secured by Visage Inc.

Google's Digital Mapping Systems patent describes 'various methods, systems and apparatus for implementing aspects of a digital mapping system'.

It includes methods for using map tiles and grids in client-server environments.