# Planar Area Calculations

Planar area is computed by projecting the cut and fill portions of the surface onto a plane and calculating the area of the projection.

## Positive Planar Area

Positive Planar Area represents the projection of the cut (map areas where the upper surface is above the lower surface) onto a horizontal plane.

## Negative Planar Area

Negative Planar Area represents the projection of the fill (map areas where the upper surface is below the lower surface) onto a horizontal plane.

 This is a contour map showing the relation between positive and negative planar area on a map. The lower surface is defined by a plane where Z = 75.