Ratios and Absolute Amounts Conveyed by a Stepped Statistical Surface
David J. Cuff, Kenneth R. Bieri · The American Cartographer · 1979
The utility of a stepped statistical surface for either choropleth style or absolute quantity themes depends on how accurately readers can estimate prism heights, and whether prism volumes affect those estimates. Testing of a stepped surface through comparison of state pairs without benefit of legend revealed that most readers respond to prism heights, not volumes. The association of values with heights is consistent for a variety of data areas and for three different themes. Even for an absolute quantity, which logically can be represented by volume, the surface, scaled by height, conveyed magnitudes with as much accuracy as scaled circles used for the same data. Altogether, the results show a stepped surface scaled by height to be a versatile device, and suggest that a surface representing values by volumes might be misinterpreted.