55Relief shown by hachures and spot heights. Depths shown by isolines and soundings.IN 1841, Congress created the Lake Survey within the U.S. Army Topographical Engineers, which later became part of the U.S. Army Corps of Engineers. The Survey, based in Detroit, Michigan, was charged with conducting a hydrographical survey of the Northern and Northwestern Lakes and preparing and publishing nautical charts and other navigation aids. The Lake Survey published its first charts in 1852. In 1882, after producing 76 charts, it had completed its Congressional mandate.8000