He subsequently was assigned to Helena, Washington, Point Reyes and Manteo as assistant, and to Mount Weather, Raleigh, Indianapolis, Salt Lake City, Portland, Baltimore, and Denver as official in charge.

He resigned from the Weather Bureau on December 11, 1920, to accept a commission as captain in the Regular Army.

He left active service, as a major, and was reappointed at the Central Office of the Weather Bureau on March 17, 1941.

His best known work (1911) dealt with the description of weather prediction with a geometric method for dividing land areas, that although known from Dirichlet Tessellation (1850) and the Voronoi Diagram (1908), apparently had never been used in meteorology for interpolation of measurements.

Thiessen polygons have also been used to estimate the areas of influence of Mayan city-states.