PLSS Maps

http://www.idwr.idaho.gov/GeographicInfo/Publications/adjudica.htm

PLSS Maps are part of the Public Land Survey System. This is the numbered system that  was used to divide land into plots in a grid system everywhere in the US except the original thirteen colonies and Texas. This PLSS map is from Boise, Idaho and shows that the grid system simply laid the grid out over the land, regardless of the geographical features there (as shown by the river). The sections are organized into increasingly smaller divisions, and are organized based on the location relative to the base lines.