Dating dos and don ts 1949

Be clear in you research question before beginning to look for map evidence.

These images were popular from about 1860 until aerial photography rendered them obsolete in the 1920s.

Plat maps are based on the Public Land Survey System (PLSS) gridlines that were established as a result of the Northwest Ordinance of 1787.

The first surveys were completed in 1820 after the establishment of the US General Office in 1812.

Orthophotographs are maps made from aerial photos with corrections made for the angle of the camera with respect to the landscape.

Many of these images can be obtained in digital format from the USGS.

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