Based on an area containing at least two points, a Thiessen Polygon is a 2-dimensional shape whose boundaries contain all space which is closer to a point within the area than any other point without the area. Such polygons are a critical component of such spatial analysis concepts as nearest neighbor and proximity assessment. Named after American meteorologist Alfred H. Thiessen, Thiessen polygons are a more specific application of Voronoi diagram to meteorology and geophysics. 
- A.H. Thiessen. 1911. Precipitation averages for large areas. Monthly Weather Review, 39(7): 1082-1084.