Estimating big crowds accurately with weather balloons, bicycles, and counting

The best way to count large crowds – such as in Washington D.C. – may be by using a weather balloon and supplementing that data:

Well, technically, a “tethered aerostat.” Tethered because it is anchored to the ground, and aerostat because it will hold a static altitude in the air. A nine-lens camera is attached to its base, so it can capture the full 360-degree view of the proceedings. It will observe the entire Women’s March…

Their technique involves more than just the weather balloon. While the weather balloon records the events from above, Westergard and his team will bike or walk around the protest site. They’ll take note of how many people are taking cover under structures, like the massive elm trees on the Mall. Sometimes they’ll even lower the aerostat so that it can capture crowds in the shade. “At 400 feet, we’re looking under the trees. At 800 feet, you’re looking at the top of them,” he told me…

Once the data is collected, they return to their headquarters. Three days of work commences. First, they will measure the density of different parts of the crowd. They do this by counting heads in a specific area. “We sit there literally, head by head, going tick-tick-tick-tick-tick” with the images, he told me. “It’s painful, it’s long, but it’s far more accurate than these algorithms.”

Sometimes they outsource this task to Amazon’s Mechanical Turk service to increase their own accuracy: They ask a dozen strangers to count heads in a certain picture without telling them where the picture was taken.

Once they have this density map, they overlay it on a map of the topography. “If you have people surrounding the Washington Monument—which is on a moderately steep hill—and you look out at a crowd, you’re going to see more people because they’re tilted toward you,” he said. The computer model will correct for those kinds of inaccuracies.

See earlier posts (such as here and here) about counting crowds.

It is also interesting that this more accurate method is explained by the leader of a private firm: “Curt Westergard…is the president of Digital Design and Imaging Service based in Falls Church, Virginia, and he stressed that his company’s methods were “at the very top of the accuracy and ethical side.”” He is working for those who want to hire him, something that could be worthwhile for the article to explore. Are they impartial observers who are doing this work for science? In other words, crowd counting could be influenced by who exactly is doing the counting. Parties who often make the counts – police, local officials, the media – have vested interests. For example, take the case of the rally for the Cubs World Series victory.

Of course, as it noted in this article, the numbers themselves are often politicized. What will be the official count accepted by posterity for a Trump inauguration that likely stirs up emotions for everyone?

Chicago sets new record for tourism

The city of Chicago may have problems but the number of tourists continues to increase:

An estimated 54.1 million visitors came to the city in 2016, up 2.9 percent from the previous year’s record-setting count. The increase marks a step towards reaching Mayor Rahm Emanuel’s goal of annually attracting 55 million out-of-towners to Chicago by 2020…

Leisure proved to be the primary attraction behind Chicago’s rising tourism numbers. About four in five visitors last year (nearly 41 million) came to Chicago for fun, city officials say…

The long-running Blues Festival, the NFL Draft and the Chicago Cubs World Series victory parade were three major events last year that helped boost tourism numbers, Kelly said…

City officials also cite business visitation, which grew by 2.1 percent from the previous year, as another factor. Some 31 major conventions and meetings were hosted citywide throughout last year, drawing nearly one million attendees; 35 business meetings are slated for 2017.

I’d love to see how these numbers were calculated. Just take the suggestion that the Cubs World Series parade and rally are part of these totals; how big were those crowds? Early estimates were high but there was little commentary later about more solid figures. Were suburbanites who came in for the day counted as tourists? If the 5 million figure holds, then this one event on its own pushed the city from a lower number than the previous year to a record number.

Skepticism of 5 million fans for Cubs parade, rally

Even though the 5 million attendees estimate for the Cubs parade and rally was widely shared after being made by city officials, there is good reason for reconsidering the figure:

“The guesstimates are almost always vast exaggerations,” said Clark McPhail, a sociology professor emeritus at the University of Illinois at Urbana-Champaign.

Politics often play a factor in overblown crowd counts. Runaway enthusiasm also could pump up the final tally, McPhail said.

There is a science to calculating crowds. The most common method is to draw a grid and make an estimate based on the average number of people that would fit into each section.

Another way to gauge crowds, particularly in a city such as Chicago, would be to analyze the capacity of buses or trains to deliver millions of people downtown or along the parade route, according to Steve Doig, the Knight Chair in Journalism at Arizona State University.

It doesn’t seem like it would take too much to draw a better estimate: there are plenty of aerial shots of the parade route and rally and groups like Metra and CTA could share figures.

Perhaps it isn’t a matter of examining the data: perhaps few people want to. Chicago could use some good news these days and making such a lofty estimate – supposedly making this the seventh largest peaceful gathering of people in human history – can boost the city’s image (both internally and externally). The team probably doesn’t mind the figure: it illustrates how dedicated the fans are (though there are plenty of other ways to do this) and might help increase the value of the franchise. The fans like such a figure because they can say they were part of something so much bigger than themselves.

If a revised lower figure gets released, I suspect it will not reach much of an audience.

Sociologists with their interests in social movements have been at the forefront in estimating crowd size. See earlier posts about counting crowds here and here.

How to count crowds accurately, not for PR

Counting large crowds is an inexact science:

“In reality, estimating the size of crowds at mass public events is much more about public relations than a quest for truth,” said Steve Doig, a crowd counting expert who is the Knight Chair in Journalism at Arizona State University.

So how can this be done well?

1. Make a grid
A credible estimate will require knowing the size of the area where the crowd is gathered.

2. Estimate density

It’s important to understand that crowds are not uniform in nature. People clump in some areas and spread out in others. Determining density helps understand how many people can realistically fit into a space…

3. Verify with other sources

A large crowd will require special accommodations. Many will choose to take public transportation to an event. Others will drive. Either way, attempt to compare the crowd-size estimate with other sources, like passenger volume data.

It is not unusual to have vested interests when acquiring data. Different sources with different vantage points – like organizers, police or officials, and the media – could produce multiple counts for a single large event. Perhaps the people with the better social position are the ones whose numbers end up carrying the day. Yet, we could have a variety of reasons for wanting to have the most accurate data including for history’s sake and in order to provide the needed local services for such large gatherings.

Just for fun, here is Wikipedia’s List of largest peaceful gatherings in history. Interestingly, there is a section at the bottom that discusses the methodology of accurate crowd counts. However, it looks like the citations for most of these large crowd counts refer to media sources which could be drawing from a variety of counters including the media itself.

The “particle” rules governing human interactions in crowds

A group of physicists suggests humans follow particular rules while interacting in crowds:

Skinner and his coauthors, a pair of computer scientists at the University of Minnesota, looked at six data sets that capture individual movements in crowded places: four from natural settings, like video footage of pedestrians on a college campus, and two from laboratory experiments, in which participants were tracked with cameras as they navigated a corridor that narrowed into a bottleneck. Such data sets have become available only in the last five years, as improvements in camera technology and the field of computer vision have made large-scale pedestrian tracking possible.

Initially the researchers assumed they would find a “repulsive force” between people, like the one that pushes charged particles apart. As they looked closer, they realized it wasn’t that simple: There was a repulsive force between individuals, but it only operated sometimes. “Two people walking head first into each other have a strong interaction,” Skinner says, “but people walking side-by-side have almost no interaction.”

So the researchers went looking for a new rule. They found it in a variable they called “time to collision,” which explained many of the course adjustments they observed. The closer two people get to colliding, the more energy they expend getting out of each other’s way. To be technical, they found that the interaction between individuals in a crowd could be described as 1 over the square of the time to collision: As a collision becomes more imminent, the energy you apply to avoiding it goes up drastically.

Unlike with particles, the mechanism that produces these adjustments is an instinctive mental calculation rather than any kind of physical force. There’s also a limit to how far out we can—or need—to account for other people’s movement. When the time to collision was more than three seconds, the researchers found that the interaction energy between two pedestrians fell to zero, meaning people weren’t taking each other into account at all.

This seems to apply mainly to areas where people are going opposite directions, whether in an open concourse at a stadium or a crowded city crosswalk with two masses of people trying to get past each other. In these situations, there is usually an area of stronger flow on each side but then in the middle – between the two larger flows – is a zone where such collisions are imminent. I know because I often walk in such zones when in a hurry. It can be difficult in those situations to avoid people and not everyone likes to walk in such high-stakes areas where there is a higher probability of bumping into people.

The article goes on to talk about applications of these findings. I would guess that means having more clearly marked traffic flows and trying to avoid the weaker flows or neutral areas that I mentioned.

Are micro-apartments bad for your health?

Micro-apartments might be a popular idea these days but some experts suggest they might be bad for the health of certain groups:

“Sure, these micro-apartments may be fantastic for young professionals in their 20’s,” says Dak Kopec, director of design for human health at Boston Architectural College and author of Environmental Psychology for Design. “But they definitely can be unhealthy for older people , say in their 30’s and 40’s, who face different stress factors that can make tight living conditions a problem.”

Home is supposed to be a safe haven, and a resident with a demanding job may feel trapped in a claustrophobic apartment at night—forced to choose between the physical crowding of furniture and belongings in his unit, and social crowding, caused by other residents, in the building’s common spaces. Research, Kopec says, has shown that crowding-related stress can increase rates of domestic violence and substance abuse…

Susan Saegert, professor of environmental psychology at the CUNY Graduate Center and director of the Housing Environments Research Group, agrees that the micro-apartments will likely be a welcome choice for young New Yorkers who would probably otherwise share cramped space with friends. But she warns that tiny living conditions can be terrible for other residents—particularly if a couple or a parent and child squeeze into 300 square feet for the long term, no matter how well a unit is designed…

“When we think about micro-living, we have a tendency to focus on functional things, like is there enough room for the fridge,” explained University of Texas psychology professor Samuel Gosling, who studies the connection between people and their possessions “But an apartment has to fill other psychological needs as well, such as self-expression and relaxation, that might not be as easily met in a highly cramped space.”

While this is largely framed in terms of negative consequences for mental health, it strikes me that a lot of these concerns are built around social expectations about private space. In modern America, people expect a certain amount of space, whether in public or at home. This reminds me of the findings in Going Solo where more and more Americans want home spaces where they can get away from relationships. But, just how much space do they need? Is the ability to handle small spaces proportional to the space in an average new house (around 2,500 square feet in the United States) or to the large living spaces usually portrayed on TV?

It seems like there should be comparative data from other countries. For examples, some European countries as well as Japan have had smaller spaces for decades. Do they have higher rates of stress and other negative outcomes?

The most used subways in the world and American complaints about crowded mass transit

Check out this list of the subways with the most riders. This is the top 10: Tokyo, Seoul, Beijing/Moscow (tied), Shanghai, Guangzhou, New York City, Mexico City, Paris, and Hong Kong. Here is how the story describes these subways:

While vital to both big-city residents and visitors, subway systems can inspire a love-hate relationship, with overcrowding blamed for much of the frustration. While we may not love riding in sardine-like train cars, we do appreciate the efficiency and even beauty of many of the world’s most popular subway stations.

I’m not sure why there is consternation about the crowded nature of these subways: are there more efficient ways to move millions of people in some of the densest areas humans have every known? If everyone could have their personal space, like in cars which Americans prefer, it becomes really hard to have cities with densities like those in the top 10. If we operate with the assumption that all humans would prefer to be in less crowded spaces if they could afford to, then this might make sense.

I wonder if such complaints in the United States about crowded mass transit betrays American sensibilities for privacy and space. While people in other countries might choose mass transit over the costs of cars (and they are expensive to operate, in addition to the space, infrastructure, and resources they require), Americans work in the opposite direction: they would prefer a car until it becomes too difficult. For example, see this discussion about getting wealthier Americans to ride buses.