Area
The geometric area of the raw geometry. This does not account for levels - you can effectively assume it is the area of the bottom level of any particular geometry.
Perimeter
The length of all sides of the raw geometry, summed.
Perimeter only calculates for closed polygons.
Length
The length of all edges of a polyline.
Length only calculates for lines.
Top
The tallest point on the geometry, measured from the ground plane.
If the geometry is stacked, Top will consider the height of any geometries below it in the Top calculation.