How Airports Serve Montana
Mark Pearson
This map displays the major airports in and around Montana. It shows how the state can divided according to which airport is the closest as the crow flies.
The flags are a sample of 271 census tracts (of 271 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/

BIL serves 229,297 people in MT
Billings Logan International Airport

GTF serves 205,374 people in MT
Great Falls International Airport

MSO serves 193,639 people in MT
Missoula International Airport

BZN serves 184,394 people in MT
Bozeman Yellowstone International Airport

GPI serves 143,672 people in MT
Glacier Park International Airport

BIS serves 28,989 people in MT
Bismarck Municipal Airport

RAP serves 4,050 people in MT
Rapid City Regional Airport

dividing line

1,743 people
closest airport: BIL

3,922 people
closest airport: GPI

1,773 people
closest airport: BZN

closest airport: BIL

closest airport: GTF

closest airport: BIS

closest airport: MSO

closest airport: GPI

closest airport: BZN

494 people

718 people

619 people
closest airport: GTF

closest airport: RAP