Navionics is a location, GPS, and mapping service. Navionics provides maps, locations, and geocodes for numerous areas and in a variety of conditions (marine, skiing, etc.).
The Navionics API allows developers to access and integrate the functionality and data of Navionics with other applications and to create new applications. Public documentation is not available; interested developers should sign up for API access here: http://www.navionics.com/en/webapi-download.