All maps are part fiction. Cartographers choose which information to include and which to reject, which relationships to focus on and which to ignore. In the case of maps for bus and train systems, usually the relationship between time and space is one that gets oversimplified during the mapmaking process.
Consider the Massachusetts Bay Transportation Authority’s (MBTA) maps for Boston’s commuter rail system. Colorful lines radiate out from urban Boston to the suburbs, punctuated by white dots for stops, evenly disbursed along the length of the route. While the diagram serves its purpose of efficiently showing commuters which routes to take, it gives no information about how far apart the stops are or how long it would take to get from one point to the other. The fact that they’re so evenly spaced may even give the sense that they’re roughly the same distance apart, which is hardly the case.
That’s what makes designer Peter Dunn’s time-scale transit maps so compelling. His first map, released this summer, re-imagined a diagram of Boston’s subway system (the T) to include information on how long it takes to travel between stops. Just this week, he released a time-scale version of the commuter rail map.
Like on any map, train routes snake out from central nodes at North and South Stations. Dunn’s addition is to organize the map around concentric circles, which indicate an increasingly longer commute time from the origin point. Each line circle indicates a minute of time, so users simply count the circles between stops to figure out how long it’d take. As he writes on his blog:
Since commuters probably already know their schedules, the diagram is potentially more useful to new riders. Car commuters can see where they might save time by taking the train. Newcomers looking for a place to move in the region can quickly compare how much of their day they’d spend commuting from various stations. (If you choose the home another six minutes away, that’s an extra hour a week you’ll spend getting to and from work.)
He also plays with the width of the route to indicate the frequency of trains on those tracks. A thicker line means more trains operate on that route. A larger circle for a stop indicates more trains stop there.
While layering on those added bits of information seems so logical, Dunn doesn’t expect the MBTA to trade out their current system for his own any time soon. He writes:
Even though time-scale maps are perfectly useful for many travel situations, they wouldn’t serve well as official system diagrams. For one thing, stretching out lines by travel time leaves a lot of empty space in between them, not an efficient design. Radial maps like this also forsake many of the geographic cues that help orient riders as directions are skewed and landmarks omitted. This map doesn’t even show connections to the subway or other modes, which is a must for any good transit diagram. Even besides these drawbacks, showing scheduled travel time ultimately just isn’t the most important job for a transit map to do.