Hassler performed a triangulation survey: measuring a base-line, measuring angles from the ends of the base-line to a distant point with a theodolite, then using trigonometry to calculate distances to that point. Hassler built triangle against triangle in this manner. The map shows Hassler's triangulations of Long Island Sound --triangles laid up one against another, advancing into the Sound from an initial base-line on the shore, an imposition of pure geometry on the winding coast .

Bust of Hassler, plaster, artist unknown