B/W folding chart showing the progress of the Triangulation in Wisconsin and Minnesota. The map and shows the main lines of triangulation made during the year ending in June 30th, 1893 in southern Wisconsin between lake Michigan and the Mississippi River, then north along the river to the Minneapolis/St.Paul area.
Triangulation in Wisconsin and Minnesota, 1893
Chart 19. Progress of the Triangulation in Wisconsin and Minnesota, June 30, 1893.