Salon.com has an interesting slideshow of the 10 most segregated cities in America.  The data comes from the 2010 Census, and the methodology to determine the level of segregation is based on differences between census tracts:

We may think of segregation as a matter of ancient Southern history: lunch counter sit-ins, bus boycotts and Ku Klux Klan terrorism. But as the census numbers remind us, Northern cities have long had higher rates of segregation than in the South, where strict Jim Crow laws kept blacks closer to whites, but separate from them. Where you live has a big impact on the education you receive, the safety on your streets, and the social networks you can leverage.

The following is a list of the nation’s most segregated metropolitan areas of over 500,000 people. The rankings are based on a dissimilarity index, a measure used by social scientists to gauge residential segregation. It reflects the number of people from one race — in this case black or white — who would have to move for races to be evenly distributed across a certain area. A score of 1 indicates perfect integration while 100 signals complete segregation. The rankings were compiled by John Paul DeWitt of CensusScope.org and the University of Michigan’s Social Science Data Analysis Network.

Each of the 10 most segregated cities includes a narrative for the city.  Several include observations on transportation and the linkages between land use and infrastructure.

# 10. Los Angeles

The L.A. riots of 1992, like the 1965 Watts riot, were sparked by police brutality, a steady concern in besieged neighborhoods like South Central. Nearly 20 years later, the jobless ghettos of black and Latino Los Angeles remain. Greater Los Angeles has been so big for so long — legion nodes connected by extensive highways — that it’s hard to say exactly what its borders are. Safe in their cars and behind their gates, most white people have gone back to not paying attention.

In short, transportation matters. Diversity without intermingling can be isolating.

# 2. New York

Ingrid Gould Ellen, an urban planning and public policy professor at New York University, says that New York City is somewhat more integrated than the data would suggest, because it is far denser than most cities. Since census tracts are made up by population, tracts in New York tend to be very small.

“What happens is that we’re not making apples to apples comparisons. The neighborhoods in Atlanta and Houston are 10 times the size of neighborhoods in New York City physically,” she says. “The census tracts are so much smaller, so you’re likely to cross over a number of census tracts every day.”

The daily commute of the average New Yorker also lessens racial isolation. Thanks to the dominance of public transit, intra-city travel tends to be a diverse experience.

New York, despite segregation, benefits from both density and transit.

# 1. Milwaukee

Nationwide, blacks have been concentrated in the inner city, far away from where new jobs are created. Yet the case of Milwaukee is extreme: 90 percent of the metro area’s black population lives in the city. Making matters worse, suburban whites are notably hostile to building any form of public transit to connect city people to suburban jobs, further exacerbating segregation’s ill effects.

If you’re wondering if this can somehow, some way, be blamed on union-busting Wisconsin Gov. Scott Walker, the answer is yes. Walker took the lead in a campaign against public transit to connect the suburbs to the city during his time as county executive. He thought the funds would be better spent on highways.

“There is virulent opposition in these exurban counties to any kind of regional transit system, particularly a regional rail system. There have been proposals over the years, but they’re always DOA,” says Levine. “Governor Walker’s big issue as state representative and county executive was ‘Over my dead body light rail,’ and he fought with Milwaukee’s mayor over funds for regional rail. He very much represents that suburban and exurban base.”

That map graphic says it all.