Illinois 1959 county gross farm product value per acre
Classic data set for the choice of class intervals for choropleth maps.
A data frame with 102 observations on the following 2 variables.
a numeric vector: Per acre value of gross farm products in dollars by county for Illinois in 1959
a numeric vector: county area in square miles
Jenks, G. F., Caspall, F. C., 1971. "Error on choroplethic maps: definition, measurement, reduction". Annals, Association of American Geographers, 61 (2), 217–244
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