Accurate vehicle positioning with respect to a geographical database is fundamental to successful use of in-vehicle navigation systems. In this paper, the authors examine known distortions in the database by their effect on vehicle positioning as measured by the Certainty Factor. The results are shown graphically as a function of distance as the vehicle traverses the distorted region of the database. Three cases are examined using two vehicle positioning algorithms - one more heavily weighted with GPS than the other. A conclusion made is that the Certainty Factor concept is a valid measure for examining database distortions as well as vehicle positioning algorithms.