Maps

Tracing the World's Most Complicated Roadways With GPS Data

How highway interchanges become beautiful color-coded open-source maps.

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OSM

The intricate highway interchange is always easier to appreciate from above. Take away the congestion, the last-minute mergers, the tail-pipe exhaust, the conflicting road signs and the vertigo, and a perfect cloverleaf really starts to look like a marvel of engineering.

Perhaps you've seen photos like these that capture the most complex Interstate overpasses as interlocking ribbons of asphalt. The above image, though, presents some of this same information in a quieter, more beautiful way, reducing interchanges – in this case, the intersection of I-70 and the I-465 beltway around Indianapolis – to their simplest geometry.

That picture comes from a layer of GPS traces on OpenStreetMap, where it's now possible to visualize the open-source mapping project's vast, ever-updating GPS database. The traces come from individual contributors, often driving their own cars, creating their own data streams via something as simple as an app on their smartphones. Such data can correct imprecise maps or validate earlier edits. But GPS data also produces a compass byproduct: Using it, we can verify the direction of a one-way street captured from a moving car, or unravel the elaborate logic of a four-way stacked overpass in a way that's not possible from a satellite photo.

Forget the old two-toned picture of road traffic: red for tail lights and white for head lights. This map, courtesy of MapBox and the OpenStreetMap Foundation, paints moving GPS traces with the full color wheel at right. Eric Fischer, who worked on the project, explained the method this way by email:

The direction works by comparing the angle between each point in the GPS track and the one that follows it. If the track says that a person was in one location and then the next point in the track is due east of there, the line between the two is colored red.

The resulting map of the world portrays every traced road by both location and direction. The highway interchanges, though, pop out as some of the most compelling parts of our infrastructure when viewed this way. With the help of Fischer, we pulled out some of our favorites below.

Consider this a more zen appreciation of highway infrastructure than what you'll undoubtedly experience on the roads this week heading to and from Thanksgiving.

The famous Spaghetti Junction outside of Birmingham in the United Kingdom:

L.A's Judge Harry Pregerson interchange:

Another four-level interchange in Los Angeles:

The confluence of I-90, I-190 and I-294 outside of O'Hare International Airport in Chicago:

I-287 and I-95 in New Jersey outside of New York City:

Another New Jersey gem, from I-95 and I-495:

The I-70 gap in Breezewood, Pennsylvania:

The Arc de Triomphe in Paris:

Also in Paris, the Place de la Nation:

A particularly heavily traveled cloverleaf in Moscow:

If you find better examples (or the rare car traveling the wrong way), please share them below.

All images courtesy of OpenStreetMap.

About the Author

  • Emily Badger is a former staff writer at CityLab. Her work has previously appeared in Pacific StandardGOODThe Christian Science Monitor, and The New York Times. She lives in the Washington, D.C. area.