How Airports Serve Washington
Mark Pearson
This map displays the major airports in and around Washington. It shows how the state can divided according to which airport is the closest as the crow flies.
The flags are a sample of 500 census tracts (of 1445 tracts total) within the state.
Some census tract flags may look like they are colored for one airport's region but are actually in another airport's region. The census tract flags are colored with which airport they are closest to as the crow flies along the surface of the earth (the Haversine distance formula). The region boundaries that are displayed on map were computed assuming assuming the earth is flat. (The lines that divide regions are a Voronoi diagram, and I couldn't find any algorithm that calculate the lines on a sphere such as the earth.) In short, although a few census tracts may look like they're mislabeled near a boundary, it's actually the boundary that is slightly wrong.
For more information, see the full report:
http://www.mark-pearson.com/airport-distances/

SEA serves 4,229,175 people in WA
Seattle-Tacoma International Airport

PSC serves 718,357 people in WA
Tri-Cities Airport

GEG serves 660,087 people in WA
Spokane International Airport (Geiger Field)

PDX serves 586,830 people in WA
Portland International Airport

BLI serves 530,091 people in WA
Bellingham International Airport

dividing line

2,503 people
closest airport: SEA

3,490 people
closest airport: GEG

3,733 people
closest airport: GEG

closest airport: SEA

closest airport: BLI

closest airport: PSC

closest airport: PDX

closest airport: GEG

730 people

956 people

5 people