THE RELATIVE EFFECTIVENESS OF SOME COMMON GRADUATED POINT SYMBOLS IN THE PRESENTATION OF QUANTITATIVE DATA

Abstract

Circles with their areas varying in direct proportion to quantities represented are a common form of graduated point symbols. When so used, unfortunately, the average map reader perceives a smaller quantitative difference than intended because circle size differences are usually underestimated. An apparent size scale developed empirically fifteen years ago is claimed to eliminate the problem of consistent underestimation. More recent investigations by psychologists and cartographers support the apparent size scale. Bars communicate quantitative variation effectively when graduated in the traditional manner on a linear basis, but wedges require an apparent size scale and even then are less accurately judged.