Sinkhole volume metric based 3m digital data.
TN topo is about 60 sq miles.
The heatmap is based on subdividing each topo quad into a 3x3 grid,
so each cell is about 6.7 sq miles.
Metric is sum of sinkhole volumes in cell.
Sutherland's
density map
based on 3m+ deep sinkholes weighted by volume.