You might guess that South Lake Union, of any neighborhood in King County, has had the most dramatic increase in population density. Close, but no cigar.

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You might guess that South Lake Union, of any neighborhood in King County, has had the most dramatic increase in population density.

Close, but no cigar.

Just east of Redmond, in unincorporated Union Hill-Novelty Hill, density has soared by 580 percent since 2000.

This had been an entirely rural area until a master-planned development — locals call it “The Ridge” — added 4,500 housing units. In 2000, there were only about 300 people per square mile there. Today, that’s jumped to more than 2,100.

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That’s not to downplay the remarkable transformation of South Lake Union. The neighborhood’s two census tracts have densified faster than any other part of Seattle — and the adjacent tract that covers Lower Queen Anne is just slightly behind. In all three, population density has more then doubled.

Seattle’s other fastest-growing neighborhoods are central Ballard, Belltown, NewHolly (in Rainier Valley), and Pioneer Square/Chinatown International District. Population density has increased by more than 50 percent in all these areas.

Bellevue’s downtown has also gotten a lot more crowded — with more than 22,000 people per square mile, it’s denser than many parts of central Seattle.

Nearly every part of Seattle has gained population in the past 15 years, but — believe it or not — there are a few exceptions. The most dramatic decline is in the south part of First Hill, where population density dropped by 28 percent. But that can be attributed to the current redevelopment of the Yesler Terrace community — thousands of residents have been relocated while that project is underway.

The densest census tract in Seattle — and for that matter, in the Pacific Northwest — has about 53,000 people per square mile. It’s located on Capitol Hill, just west of Cal Anderson Park.

Explore the data for yourself. This map of King County census tracts is color-coded to reflect the percent change in population density since 2000. Zoom into your neighborhood and click on a tract to see the underlying data.

The source for the data is the Washington Office of Financial Management.