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 Also for the first time, the Census Bureau developed guidelines for measuring waters other than inland water; that is, coastal water, large embayments, sounds, straits, and the Great Lakes.

From its 1950 through its 1970 censuses, the Census Bureau used the same techniques to obtain updated area measurement data; each decade it revised the previous figures to take into account new geographic entities, shifts or transfers of territory, new reservoirs, better maps, and reported errors and inconsistencies. To perform these updates, it used information available from Federal, State, and local governmental sources. Where necessary, it remeasured geographic areas with polar planimeters or an electromechanical scanning device, the Map Area Computer. After the 1960 census, the Census Bureau published a series of reports to update the 1940 area measurement data. The 1940 area measurement values, at the county level, were treated as control figures for the 1950, 1960, and 1970 updates; that is, all geographic entities comprising a county had to equal the county’s total area figure.

For the 1980 census, there were two major changes: an improved map base and the first use of computer processing techniques to obtain updated area measurements. The Census Bureau recalculated the area of every State and county from the largest scale USGS topographic maps available, usually the 1:24,000-scale series. (For Alaska, the 1:250,000-scale maps were used.) The Census Bureau obtained the new area measurement values digitally; that is, by a process that converted boundaries on maps into x, y coordinates based on a grid network (latitude/longitude). The digitized values, stored in a computer file, were processed to provide improved area measurement figures for States and counties. To obtain measurements for other geographic entities, such as places and MCDs, and for water bodies, the Census Bureau used a variety of sources: local estimates of area, State highway maps, individual maps of places, the Metropolitan Map Series, and the records of governmental agencies that control development of new reservoirs and similar water bodies. Notes and References Area Measurement/Water Classification15-3