1. A method for ascertaining at least one exit probability from a land area identifiable in a digital map as open terrain, starting from a position within the land area, the method comprising: subdividing the land area into a plurality of cells, with an initial transition probability being assigned to at least one transition from one of the cells to an adjacent one of the cells, the transition being situated between the position and an edge of the land area; adapting the initial transition probability of the transition, in response to a presence of at least one item of information from the digital map to obtain an adapted transition probability for the transition, the item of information being associated with one of the cells or with the adjacent cell, wherein, in the adapting, the initial transition probability is adapted using a distance of a transition from an entry point of the vehicle into the open terrain so that the initial transition probability is adapted to a higher probability in dependence on the distance of the transition; and ascertaining the exit probability, the exit probability being ascertained using the adapted transition probability, wherein the method is performed by a car navigation system.