As Chicago’s construction boom continues, delivering thousands of new apartment units, hotel rooms, and millions of square feet of new office space in this latest cycle, urban planners are taking notice of the changing population density in Chicago and other major cities throughout the country. According to a new report from the New York Times, which studies data gathered by the U.S. Postal Service and 2016 Census, Chicago has become noticeably more dense in the last several years. However, many other cities witnessing major construction booms have not experienced the same trend.

Between 2010 and 2016, Chicago’s density has increased by 1.2%. It may not seem like much, but considering Chicago’s stagnant population growth, the report suggests that the Windy City’s population is shifting and refocusing in the city center. Middle class black families are leaving Chicago while younger, more affluent residents are flocking into areas like the Loop, the West Loop, and Wicker Park. The only major city that has become more dense in the same time period? Seattle.

It’s interesting to see Seattle and Chicago take the top two spots on the charts, especially when considering that Seattle led the nation for active tower cranes by the end of 2016, with Chicago following closely behind. Seattle’s construction boom is very real as the city is on track to have another record-breaking year for completed projects. Meanwhile, Chicago developers are on pace to deliver nearly 6,600 apartments in 33 different projects this year alone.

However, the story is very different in southern cities. According to the report, many major cities have actually become less dense between 2010 and 2016. Cities like Las Vegas, Houston, and Austin—metros that have all experienced increases in their population in recent years—have actually continued the trend of sprawling versus building up. Texas cities aren’t the exception however. The major metros that lead in sprawl are all located in the Sun Belt. As cities like Seattle, Chicago, and New York continue to pack more people into their city centers, Sun Belt metros are spreading further out.