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The Science Of A Great Subway Map

Researchers at an MIT lab have devised a way to determine how well straphangers can comprehend a subway map in a single glance. Massimo Vignelli really did know what he was doing.

[Image: Courtesy MBTA/Massachusetts Department of Transportation]

The most famous New York City subway map is the one New Yorkers rejected. That would be Massimo Vignelli's system map from 1972. Vignelli's modernist design stressed visual clarity over geographical precision; all the lines ran vertical or horizontal, for instance, and rectangular Central Park was rendered as a square. Public pressure led subway officials to replace the map in 1979 with one much less distorted in style but also far more cluttered to the eye.

Transit maps have a considerable impact on the everyday lives of people in cities. Traveling in and around busy urban environments can be tough for anyone—from the tourist visiting for the first time to the native heading into an unfamiliar part of town. So establishing whether a map like Vignelli's has merit despite its detractors is a matter of real consequence: the quicker people process information on a subway or bus map, the easier their lives will be.

Recently, some vision scientists at MIT developed a remarkably direct way to perform just this type of map evaluation. The research team, led by Ruth Rosenholtz of the Computer Science and Artificial Intelligence Laboratory, devised a computer model capable of determining how well people will comprehend a subway map (or any other complex diagram) in a single glance. The model spits out alternate visualizations called "mongrels"—twisted images that represent how our brains actually process the maps in front of our eyes.

The MIT mongrels draw on new scientific insights into peripheral vision. Research by Rosenholtz and others has suggested that peripheral vision operates by pooling together information outside a person's direct line of sight. These peripheral pools sacrifice detail for overall impression to reduce the amount of data we process; they're a little like a low-resolution JPEG in that sense. So the mongrels effectively show what visual elements—color, text, space, line orientation, among them—have been condensed into pools during the map's journey from eye to brain.

"What these mongrels try to capture is this qualitative information about what you lose in the periphery," Lavanya Sharan, a postdoc who collaborated on the work, tells Co.Design. "Looking at these mongrels is a way of confirming the designer's intuition."

Being located in Boston, the researchers took a particular interest in the Massachusetts Bay Transportation Authority’s recent contest to redesign the subway map. Earlier this month, the M.B.T.A. announced the winning entry, designed by Michael Kvrivishvili, which will begin to appear in stations next year. Rosenholtz, Sharan, and graduate student Shaiyan Keshvari created mongrels of both the current map and the contest winner to see whether or not the city was getting a visual upgrade.

Here's the current M.B.T.A. subway map:

Image: Courtesy MBTA/Massachusetts Department of Transportation

And here's the mongrel, computed for a person who's looking directly at the Kendall/MIT stop on the red line:

Image: Courtesy of the Computer Science and Artificial Intelligence Laboratory at MIT

The mongrel betrays several problems with the current map design. The silver line has disappeared into the Atlantic Ocean; it was far too light. Southern branches of the green and red lines, while perhaps geographically accurate, have become difficult to track. Many of the angled station names are a terrible blur, and the busy area between the orange and red lines is a total smear.

Now here's the contest winner:

Image: Courtesy of Michael Kvrivishvili

And here's its mongrel, also based on someone looking right at Kendall/MIT:

Credit: Courtesy of the Computer Science and Artificial Intelligence Laboratory at MIT

A few things stand out right away. The subway lines take sharper turns that are easier to follow, especially the four now-parallel green line branches. Major transfers are also a bit more crisp as a result. The station names, now nearly all horizontal, can be distinguished (if not read). The map isn't perfect—the silver line remains hard to spot at first—but from a perspective of peripheral vision the map does seem like an improvement.

"You can see that it preserves a lot of the information from the original map," says Sharan, "but it lays it out in a way that's slightly more soothing for the eye."

Of course, unless people are running for a train, they generally don't have to absorb everything about a subway map in a single glimpse. But the basic lesson still applies: a map need not stay geographically faithful to be visually useful. In certain other real-world applications, this understanding might be critical; designing in-car navigation maps that take peripheral vision into account could potentially save lives.

As for Vignelli, public opinion does finally seem to be swinging his way. In late 2011, the Metropolitan Transportation Authority of New York introduced a weekend service map designed by Vignelli in his 1972 style. The MIT lab has shown the wisdom of this choice by creating mongrels that compare Vignelli's weekend map to the regular weekday map:

Image: Courtesy of the Computer Science and Artificial Intelligence Laboratory at MIT

The daily map, geographically inclined just as the public wanted back in the 1970s, is a mess. The diagrammatic Vignelli weekend map, meanwhile, hardly looks like a mongrel at all—a sign of the designer's preternatural understanding of visual processing. Intuition confirmed.