The new population figures show slow growth in Seattle and big growth in outer counties

Growth in greater Seattle was actually a little lower (9.4 percent) than in the rest of the state (11 percent), contrary to what you would think from the local media. Our local growth was fueled by both continuing job growth but also by our popularity with the confident young. This local growth is a little slower than might be expected from the job opportunities, partly because of the high cost of living, especially housing. Fastest growth is in Clark County (suburban Portland), the next tier of counties beyond the core four counties of King, Kitsap, Pierce, and Snohomish: That is, in Thurston, Skagit, and Kittitas, and beyond in Whatcom (Bellingham), and in Benton and Franklin (the Tri-Cities of Kennewick, Richland, and Pasco).

Again, contrary to recent headlines, the growth of the city of Seattle was very modest, and the population is still below its maximum of more than 600,000 back in 1955, at the height of the baby-boom. With a vast amount of construction all around, you might find this hard to believe. The explanation is that housing units are increasing much faster than population, because of the loss of families to the suburbs and beyond and the small average household size in the city (apartments and condos average fewer than two persons per unit). This is not so much because of dissatisfaction with the schools, as is often claimed, but rather with limited housing choices and high costs for families.

The rest of King County is growing more than twice as fast as Seattle, adding almost five times as many people. And because of a shortage of land for single-family houses and high costs in King, growth is much faster in suburban Pierce and Snohomish than it is in King County. Seattle now has one-sixth of the metropolitan population, and only 7.5 percent of metropolitan growth, even while it gets probably 75 percent of regional investment in transportation. Pretty amazing leverage! A combination of growth management and of demographic change has led to population resurgence in our core cities and in containment of growth within the designated urban footprint. But the real story is one of decentralization and leapfrogging spillover, despite the rhetoric and strong planning forces for concentration.

Oregon's (and Portland's) growth is about the same rate as Washington's (and central Puget Sound), which might reflect the fact that the data for Oregon are for 2006 rather than 2007. Alaska's growth rate is rather low. Idaho's (especially Boise's) is very impressive.

The story of natural increase (difference between the number of births and of deaths) and net migration (difference between the number arriving and the number leaving) is quite interesting. For a seven-year period, a natural increase share of the base population under 5 percent is quite low, meaning a combination of low birth rates and/or high death rates — not because of poor health, but because of an aging population. The higher rates of natural increase for Clark, the Tri-Cities, Idaho, and Alaska reflect a younger, more familial and traditional population, as well as ethnic differences.

Now, there is no such thing as a "net migrant" (for example, Washington's net migration of 343,000 could be the result of 600,000 moving out and 943,000 moving in). But net migration greater than natural increase suggests fairly significant growth. The figure for net migration barely balances in greater Puget Sound (157,000 to 150,000), but is a lot higher in the rest of the state (186,000 to 150,000), as well as in Oregon and in Idaho.

Population growth and net migration in Washington are concentrated along two corridors: Interstate 5, in the form of spillover from both Seattle and Portland, in part seeking more space and lower costs for business and for housing; and in the Columbia River valley, north from the Tri-Cities. Clark (Vancouver), Benton and Franklin (the Tri-Cities), Thurston (Olympia), and Kittitas counties are high on natural and net migration, while several more rural, natural-amenity-rich counties like San Juan, Jefferson, Clallam, and Pend Oreille enjoy high net migration rates that overcome their natural decrease (more deaths than births, owing to their high share of the elderly).

Part of the story of population for Seattle, the region, and the state, suggested by the figures, is the unusual degree of flux, the high rate of population turnover, and even of resettlement of longer-term residents. The city of Seattle is the extreme case of this restlessness, because of the dominance of young adults, mainly not in families, of renting rather than owning, and of rapid change in home prices and apartment rents.

One last cautionary comment on population data. If you go to the U.S. Census Bureau or the Washington Office of Financial Management sites for the population data, you will see exact values like 1,737,046 for King County and 47,614 for net migration. Don't even think about believing any such precision. Such seeming accuracy is just the way their algorithms work. In reality there is an embarrassingly large uncertainty, certainly in range of tens of thousands for King county.

• Richard Morrill is emeritus professor of geography at the University of Washington. You can reach him in care of editor@crosscut.com.