6. PLSS Map

http://nationalatlas.gov/articles/boundaries/a_plss.html

A PLSS map stands for Public Land Survey System, a surveying method that spatially identify land parcels by subdividing public domain lands. It is used to locate area, identify land ownership and is actually measured on ground by surveyors. Typically, PLSS map divides the land into 6-mile-square townships, then subdivided into 36-one-mile square section, and sections can be further divided into quarter sections. North to South zones are townships and East to West zones are ranges. As seen in this map in the off white/grey states, PLSS covers the majority of the U.S. but it does not cover the original 13 colonies, Texas, and parts of Florida, Louisiana, New Mexico, and California. This map also shows the principal meridians and baselines of the PLSS, separating each patch of color by different regions.