How large is Aroostook County? Exploring the historical mutability of US county area measurements

Area measurements play a prominent role in many types of geographical and historical analyses. The accuracy and precision of such measurements, however, are dependent on a host of input factors, including the type of instrumentation used as well as the scale and projection of the source map and its level of cartographic generalization. As a consequence of variability in these inputs, published area measures change over time. This paper reviews the record of land area measurements for counties published by the US Census Bureau between 1880 and 2000, documents the major changes in measurement instrumentation and procedures employed, and analyzes patterns of the greatest variability in reported values. Two states are used as case studies (Iowa and Maine). The results suggest that the greatest variability occurs in those areas with irregular borders, thus reflecting the interaction of the source maps with human measurement error and the encoding capabilities of the area measurement instruments. The observations also indicate that variability in area measurements for counties has decreased over time.