Much of what we know about how people move around a metro area – whether they drive to work, where they're going, how many stops they make along the way – comes from travel diaries that sample households periodically fill out. Increasingly, we can supplement this information with meta-data from new sources like social media, cell phones, or electronic transit fare cards.
But the old-fashioned household travel survey still does the best job of nailing down the details: whether that traveling dot seen from a Foursquare visualization is on a bus or in a car, if she has a job, how much money her household makes. Travel surveys make it possible to disaggregate commuting patterns by income or age group.
To give a sense of what that data looks like – and what kind of patterns emerge from it – UC Berkeley planning Ph.D. student Fletcher Foti animated some of the results of the most recent surveys from the San Francisco Bay Area, Los Angeles, and New York. Here, you can watch thousands of these households move about the day described in their travel diaries (all of the responses are compressed into one day). Foti has has placed each dot representing an individual person at a random "home" location within its assigned Census tract to protect the privacy of people who completed the surveys.
His animation (which pauses briefly at each hour) is also sortable by income:
The travel surveys account for each member of a household, and Foti has scaled the dots by age (smaller dots are younger, larger ones older). In some cases, you can actually watch children leaving home in the morning with a parent.
Comparing the cities to each other, it's clear that Los Angeles commuters rely much more on cars than New Yorkers. It's also apparent that New Yorkers work way later than San Franciscans. They tend to flock out of downtown between 7 and 8 p.m., some even later. San Francisco's downtown, on the other hand, is pretty cleared out by 5 p.m.
"And it’s true, it’s absolutely 100 percent true," says Foti, who also co-founded an urban data visualization firm called Synthicity.
Sort the data by income, and you can watch lower-wage commuters in all cities work late-night shifts in the service industry.
"One of my favorite things to do in New York is go to highest income, zoom out pretty far, and you just watch the highest income group flood into downtown and then go home," Foti says. "The commute distance is enormous"
Here are sleeping households, in the middle of the night, making less than $15,000 a year:
And here are those making more than $200,000:
In the next few hours, many of those people will become blue dots, heading into the city by car. Their long commutes contradict the notion that it is low-income people, priced out of homes in the city, who must travel the farthest to get to work.
"But we assume that it’s by choice," Foti says of the high-income commuters, "to get out to their houses in the suburbs."