1. A computer-implemented method comprising: receiving information about a plurality of prior vehicle trips along a plurality of roads in a geographic area, the plurality of prior vehicle trips involving a plurality of drivers of vehicles and each reflecting actual prior behavior of one of the plurality of drivers in traveling between a starting location in the geographic area and an ending location in the geographic area, the received information including, for each of the prior vehicle trips, indications of multiple data samples reported by a device in the vehicle as the vehicle travels between the starting and ending locations for that vehicle trip, each of the data samples indicating a road location and an associated time when the vehicle is at the indicated road location; automatically analyzing the received information about the plurality of prior vehicle trips to determine multiple compound links that each represents a preferred path between two locations in the geographic area based on actual prior behavior of the plurality of drivers, the automatically analyzing being performed by at least one of one or more programmed computing systems and including: determining based on the plurality of prior vehicle trips multiple decision points along the plurality of roads that each corresponds to a connection of multiple roads which at least some of the plurality of prior vehicle trips arrive at and continue past during those at least some prior vehicle trips, the at least some prior vehicle trips that arrive at each of the determined multiple decision points being part of at least one of traffic diverging among the multiple roads of the connection for the decision point and of traffic converging from the multiple roads of the connection for the decision point; identifying multiple pairs of the determined decision points, each of the identified decision point pairs including one of the determined decision points as a starting point and including another of the determined decision points as an ending point, each of the identified decision point pairs further having multiple alternative paths along the plurality of roads from the starting determined decision point to the ending determined decision point and having multiple associated prior vehicle trips from the plurality of prior vehicle trips that each include one of those multiple alternative paths, each of the multiple alternative paths being traveled by at least one of the associated prior vehicle trips; and selecting multiple of the identified decision point pairs to represent the determined multiple compound links, each of the selected decision point pairs having a preferred one of the multiple alternative paths for that decision point pair that is used by a majority of the multiple associated prior vehicle trips for that selected decision point pair such that at most a specified minimum amount of those multiple associated prior vehicle trips use an alternative path other than the preferred one path, the determined multiple compound links being the preferred one paths for the selected decision point pairs; and providing information about the determined compound links to enable future routing decisions for other vehicles to use the determined compound links as part of preferred routes. after the determining of the multiple compound links, automatically using the determined compound links to improve routing of additional vehicle trips through the geographic area, the using of the determined compound links being performed by at least one of the one or more programmed computing systems and including, for each of multiple requests for a route between two indicated locations in the geographic area: selecting one of multiple alternative paths between the two indicated locations for the request based at least in part on the selected one alternative path including at least one of the determined compound links; and providing the selected alternative path as the route for the request.