It isn't always easy to spot income inequality. The disparate distribution of money among a population based on race, gender and other factors could take place in your own neighborhood, and you may not even realize it. Even when college courses and movements, such as Occupy Wall Street, try to teach people about the subject, it still remains difficult to comprehend.

On Google Maps, however, it's pretty simple to see definitive lines of income inequality. And the tool can help us better understand how this inequality affects the integration of communities.

Tim De Chant came across this phenomenon last month. De Chant is a journalist and ecologist who writes about population density and urbanization on his blog, Per Square Mile. He came across a March 2008 study that showed a correlation between tree density and income in urban areas.

According to the authors of the study, who surveyed 210 U.S. cities with populations greater than 100,000 people, when the population's average income increases in a given area, the demand for trees also increases. Therefore, wealthier neighborhoods often have denser tree cover than poorer areas, making the tree a luxurious commodity.

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The geographic contrast might not be readily apparent when walking from neighborhood to neighborhood, but since Google has taken satellite images to help users plan routes and preview destinations, it's possible to see from space.

"I spent a lot of time in grad school staring at satellite images and aerial photographs, so turning to Google Maps is almost second nature at this point," De Chant tells Mashable. "When I wrote about the original study, the results seemed intuitive. They jibed with what I’ve experienced walking through various neighborhoods. But it wasn’t until a day or two after I published that article that it struck me that I could tell this story another way, through images."

De Chant found examples across the world — Rio de Janeiro, Houston, Chicago, Beijing — and took screenshots from Google that proved the forest cover-to-wealth correlation. In each pair of city images below, the first shot pictures an aerial view of the lower-income neighborhood, while the second depicts an area of higher wealth in the same city.

Rio de Janeiro

Rocinha:

Zona Sul:

Houston

Fourth Ward:

River Oaks:

Chicago

Woodlawn:

Hyde Park:

Beijing

Fengtai:

Chaoyang:

De Chant then turned to his readers, asking for images that show income inequality by tree cover. He received hundreds of images. "The response has been unbelievable," he says. "I'm still getting emails on a daily basis."

But does this information really correlate, or might the abundance of trees cause wealth? De Chant says many of his readers posed this question.

"The study says the relationship between tree cover and income is purely correlational, and I agree — to a point," De Chant says. "Trees [also] provide numerous benefits that can save people money, which would make them wealthier in real terms, even if their incomes didn’t rise. Shade can reduce cooling costs in the summer. Trees filter out particulate pollution, which in turn reduces asthma incidences, cutting health expenses. They reduce stress and make people more productive at work. Tall trees also reduce crime, which can definitely help your bottom line if you live in a robbery-prone neighborhood."

Whether it's causal or correlational, the relationship between urban environments and income inequality exists, and it extends past tree cover.

“Our cities haven't developed according to some natural law of urbanization or according to some invisible hand. They have been shaped by big and small decisions, many of them bad.”

Interboro Partners, a New York City-based firm of architects, urban designers and planners, has conducted innovative projects focusing on such inequality. While the Interboro team members, led by Tobias Armborst, Daniel D'Oca and Georgeen Theodore, are designers first and foremost, they're also researchers and teachers.

One of Interboro Partners' noted projects is The Arsenal of Exclusion & Inclusion, which began online and will become a book this fall. It documents 101 ways cities bring people together, as well as keep them apart.

"The first point to make is that our cities haven't developed according to some natural law of urbanization or according to some invisible hand," Armborst, D'Oca and Theodore write collectively in an email to Mashable. "They have been shaped by big and small decisions, many of them bad."

The partners explained that suburbanization probably wouldn't have bloomed without federal mortgage insurance, the mortgage deduction or the Interstate Highway Act. Nor would the suburbs be so segregated were it not for policies that made it easy for suburban communities to write and enforce exclusionary zoning codes, even when they violated the Fair Housing Act.

"The point is that things don't 'just happen.' Behind every outcome in the built environment is a decision and tool crafted to enforce that decision," says Interboro Partners.

Interboro Partners hasn't witnessed tree cover as a major exclusion, but the natural environment often plays a role. The partners tell Mashable about a book called Landscapes of Privilege by James and Nancy Duncan, which tackles the issue of "how the aesthetics of physical landscapes are fully enmeshed in producing the American class system." The authors write that when a town called Beford, N.Y. faced development in the 1970s, residents suddenly became concerned with the surrounding wetlands, feigning an interest in the environment to be exclusionary.

It may be difficult to see inequality through the environment in denser cities, or even in neighborhoods with different climates that aren't inhabitable for trees. However, it's still there.

"The comparison works when it's relative...You can't compare a neighborhood in Chicago to one in Las Vegas."

"Manhattan is a good example of where the relationship between trees and income falls flat — sort of," De Chant says. "The wealthy parts of Manhattan still have more trees close at hand — think Fifth Avenue across from Central Park. Obviously Manhattan has fewer trees than the Hamptons, but most wealthy parts of Manhattan still have more trees than the less well-to-do parts. The comparison works when it’s relative. For example, you can’t compare a neighborhood in Chicago to one in Las Vegas. They’re totally different climates."

Along Baltimore's Greenmount Avenue, north of 33rd Street, the line of income disparity is extremely prevalent in the Waverly, Oakenshawe and Guilford communities. D'Oca of Interboro Partners tells design radio show 99% Invisible that it's not the avenue itself that separates these neighborhoods, but the small and subtle weapons of exclusion along the way.

According to D'Oca, Waverly is around 80% African-American — 16% have a bachelor's degree and the median income is $40,000. Oakenshawe and Guilford are 7% African-American — 75% have a bachelor's degree and the median income is $75,000.

A look these communities on Google Maps reveals various barriers that may be hard to see otherwise. For example, there are only two crosswalks in the 2.5-mile stretch. By car, it's easy to make a right-hand turn into Waverly from Greenmount Avenue, but it's nearly impossible to turn left into the wealthier area of Oakenshawe (see screenshots below). Even more, the neighborhood of Guilford has long, narrow, winding roads that make it difficult to enter and leave, whereas Waverly maintains a grid-like street layout.

Baltimore

Aerial view of Greenmount Avenue (center), with Waverly to the east, Oakenshawe to the west and Guilford slightly north of Oakenshawe:

Prevention from entering Oakenshawe:

Guilford once pioneered the use of segregationist covenants, keeping the neighborhood exclusive to white people. Although this was deemed illegal in 1968, the fact that these barriers still exist prevents complete integration.

Interboro Partners plans to change this culture of urban exclusion, first by documenting it. "By denaturalizing or exposing the constructed-ness of the built environment, I think we can take a progressive position — in fact, an optimistic one — that we as architects, planners or just people can actually reconstruct and change the city in ways big and small with the right tools," D'Oca tells Mashable. "The city is makeable."

With that in mind, the average person can use Google Maps and other tools to educate herself about the visual and tangible aspects of income inequality, and even about communities at large.

"I realized that if you studied density, you could study anything," De Chant says. "It’s a perfect lens through which to view the world...The idea that knowing more about density in all forms — population density, the density of parks and open space, the density of language, even — could help us understand the world around us."

Thumbnail image courtesy of iStockphoto, groveb.