How Airports Serve Illinois
Mark Pearson
This map displays the major airports in and around Illinois. 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 3115 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/

ORD serves 4,663,093 people in IL
Chicago O'Hare International Airport

MDW serves 4,226,352 people in IL
Chicago Midway International Airport

STL serves 1,046,824 people in IL
Lambert-St. Louis International Airport

BMI serves 966,596 people in IL
Central Illinois Regional Airport at Bloomington-Normal

PIA serves 732,124 people in IL
General Wayne A. Downing Peoria International Airport (was Greater Peoria Regional Airport)

MLI serves 429,531 people in IL
Quad City International Airport

EVV serves 428,229 people in IL
Evansville Regional Airport

MSN serves 262,431 people in IL
Dane County Regional Airport (Truax Field)

IND serves 40,685 people in IL
Indianapolis International Airport

MKE serves 29,648 people in IL
General Mitchell International Airport

CID serves 5,119 people in IL
The Eastern Iowa Airport

dividing line

5,669 people
closest airport: ORD

6,288 people
closest airport: ORD

3,763 people
closest airport: ORD

closest airport: MDW

closest airport: PIA

closest airport: STL

closest airport: MSN

closest airport: BMI

closest airport: MLI

closest airport: EVV

closest airport: IND

closest airport: MKE

709 people