The use of "radar charts" is an increasingly popular way to present spatial data in a visually interesting format. Some authors recommend using "filled radar charts" to compare the performance of observational units. Filled radar charts are not appropriate for such comparisons because the size of the area within the polygon is not invariant to the placement of the measures on the axes. As a result, altering the placement of the measures on the axes can result in reversing the order of observations or reversing the order of the same observation over time.