# Voronoi Diagram

In mathematics, a Voronoi diagram is **a partition of a plane into regions close to each of a given set of objects**. In the simplest case, these objects are just finitely many points in the plane (called seeds, sites, or generators). … Voronoi cells are also known as Thiessen polygons.

The partitioning of a plane with points into convex polygons such that each polygon contains exactly one generating point and every point in a given polygon is closer to its generating point than to any other. A Voronoi diagram is sometimes also known as a Dirichlet tessellation. The cells are called Dirichlet regions, Thiessen polytopes, or Voronoi polygons.

Voronoi diagrams were considered as early at 1644 by René Descartes and were used by Dirichlet (1850) in the investigation of positive quadratic forms. They were also studied by Voronoi (1907), who extended the investigation of Voronoi diagrams to higher dimensions. They find widespread applications in areas such as computer graphics, epidemiology, geophysics, and meteorology. A particularly notable use of a Voronoi diagram was the analysis of the 1854 cholera epidemic in London, in which physician John Snow determined a strong correlation of deaths with proximity to a particular (and infected) water pump on Broad Street (Snow 1854, Snow 1855). In his analysis, Snow constructed a map on which he drew a line labeled “Boundary of equal distance between Broad Street Pump and other Pumps.” This line essentially indicated the Broad Street Pump’s Voronoi cell (Austin 2006). However, for an analysis highlighting some of the oversimplifications and misattributions in this folklore history account of the events surrounding Snow and the London cholera incident, see Field (2020).

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