In the U.S., states were surveyed using a system including township, range, and section, with the townships grouped within the boundaries of counties. Unless a township Is at the edge of a physical or political unit, the township normally is 36 square miles (sections) in size.  The Michigan atlas block has been established as a quarter township, which is 3 miles square (4.83 km). This system is in use in Michigan because it corresponds to the format of established land surveys and is similar in size to the atlas block used in most eastern states (5 km square). 

All observations must be reported for the atlas block in which the observation was made, whether you survey a small portion of the block or all of it.  Accurate Identification of the atlas block is extremely important. Each township is identified by township and range designations that can be found at the edges of most maps. Also, you will need to identify the quarter township using a numerical code assigned to each block. Beginning with the NE quarter township and moving counter-clockwise the blocks are NE=1, NW=2, SW=3, SE=4. Determine which quarter township your observations are being made and indicate this information on your checklist or casual observation forms.

Please note:  Land along the Detroit and Rouge rivers was settled prior to the traditional surveys, and land was granted by French explorer Cadillac in the form of ribbon farms -- narrow but deep lots that all had river frontage.  Because of this, official survey maps of Wayne Co. do not entirely conform to the township-range-section format.  However, for the purposes of the Atlas, the entire county has been divided as if it was entirely surveyed using the township-range-section system.  Areas affected include most of the city of Detroit, and areas along the Rouge River, and Grosse Ile.  Please request a map for these blocks from Julie Craves.