"In mathematics, a Voronoi diagram is a partitioning of a plane into regions based on distance to points in a specific subset of the plane." [0]

Here, the points are airports. There was a related discussion yesterday about a similar project. [1]

[0] https://en.wikipedia.org/wiki/Voronoi_diagram

[1] https://news.ycombinator.com/item?id=17337600