1. A computer-implemented method for determining a public transit route of a journey from a starting location to a target location, the public transit route using at least one public transportation system having public transportation vehicles, the method executed by a computer and comprising: storing in a first database transfer patterns for the at least one public transportation system, each stored transfer pattern describing a route between a pair of transit stations associated with the at least one public transportation system and comprising at least one transfer between the public transportation vehicles at transit stations located between the pair of transit stations; storing in a second database, information describing public transit stations, including for each public transit station a location; receiving from a client device a request for a public transit route from the starting location to the target location, the public transit route to include directions from the starting location to the target location using the at least one public transportation system; determining using the second database the transit stations of the at least one public transportation system that has locations within a radial distance of the starting location thereby generating a source station list that comprises the transit stations within the radial distance of the starting location; determining using the second database transit stations of the at least one public transportation system that has locations within the radial distance of the target location thereby generating a target station list that comprises the transit stations within the radial distance of the target location; for each pair wise combination of transit stations that includes one source station from the source station list and one target station from the target station list, retrieving from the first database of stored transfer patterns a stored transfer pattern that describes transfers of public transportation vehicles of the at least one public transportation system at intermediate transit stations between the source station and the target station in the pair wise combination in order to travel from the source station to the target station; for each retrieved transfer pattern, determining at least one optimal public transit route from the source station to the target station that is an instantiation of the transfer pattern at a specific time; and transmitting information describing the at least one optimal public transit route to the client device.