In the New Yorker, Nick Paumgarten on cartography and the digital revolution, that is, on MapQuest, googlemaps and the like.
It can be amusing to see what MapQuest an its ilk come up with. They don’t always work For example, I recently looked to see ho MapQuest would get me from East Ninety-sixth Street in Manhattan to the North Shore o Long Island, an hour-long trip that I an countless other drivers have honed (wit variations for personal preference, traffi avoidance, and monotony-breakage) over th years. Triborough Bridge to the Grand Centra Parkway to the Whitestone Expressway to th Cross Island Parkway to the Long Islan Expressway. Bing-bang-boom. MapQuest ha an unprecedented suggestion: take th Triborough Bridge to the Bruckner Expresswa and then to the Throgs Neck Bridge. From th Upper West Side, a few traffic lights west MapQuest, snickering, guides you to the Cros Bronx Expressway and then to the Throg Neck. The Cross Bronx? It would seem that the algorithms are new to the area. These directions involve a disconcerting degree of noncontiguousness. Why cross a body of water at its widest possible point? Why even mess with the Bronx? You may as well stick a sandwich in your ear before putting it into your mouth.
Generally, MapQuest and OnStar choose a road based on their calculations of which will get you there fastest. The criterion is time, a function both of speed and of distance. They do not, as some people suspect, simply pick the shortest route; otherwise, you might spend all your time on side streets, stuck at traffic lights or goat crossings. The algorithms consider the length of a road segment and the expected speed of the road and calculate the time it will take you to pass along it. Every road segment has a “costing,” a sum of the features that can slow a driver down. Turns, merges, exits, toll plazas, stoplights, speed zones: they all carry a cost. (Navteq has five “functional classes” of road, ranked according to connectivity and speed. An interstate highway is a one; a local street is a five.) These systems do not yet take into consideration traffic, construction, weather, time of day, or one’s tendency, on certain roads, to go faster than the speed limit.