Interface layer for navigation system

An improved method and system that provides for a data access interface layer in a navigation system. The navigation system is of the type that includes a navigation application software program that provides navigating features to a user of the system and a geographic database stored on a computer-readable storage medium wherein the geographical database includes information relating to the geographical region about which the navigation system provides the navigation features to the user. The data access interface layer is preferably stored in the navigation system as a library of software functions. The data access interface layer operates in conjunction with the navigation system application software. The data access interface layer isolates the navigation application software from the geographic data which are stored on the storage medium. The data access interface layer intercepts requests by the navigation application software for geographic data. The data access interface layer retrieves geographic data from the storage medium and converts the data into a format usable by the navigation application software. The data access interface layer also provides for memory management that facilitates accessing and using geographic data from the particular storage medium quickly and efficiently. By recognizing that different media types have different physical formats, the data access interface layer accommodates and isolates the differences so that the portions of the data access interface layer that interact with the navigation application software can be generic.