Why are so many topographic maps covered with spidery red grids and mysterious numbers and codes like "T21W"? They're part of the arcane, historic and very handy public land grid, surveyed by the U.S. government for more than 200 years. I've prepared a feature that explains the system, including the boustrophedonic numbering scheme for township sections, andbut maybe I'm getting ahead of you. Just see for yourself.
Section divisions Geology Guide image