How to calculate overcut area from a cutblock permit

Overcut is the gap between what a permit allows and what got cut on the ground. The math behind it isn't hard, but getting a number you can defend in a compliance file takes a few deliberate steps, done in the right order.

Start with the permitted boundary, not the cruise

The permit package usually comes with a shapefile or KML of the approved cutblock, drawn from the harvest plan the licensee submitted and the agency approved. Use that polygon as your reference boundary. The timber cruise and the block sketch in the harvest plan summary are drawn to a looser standard and will throw your number off by more than survey noise.

Pull the coordinate system off the permit metadata before anything else. Provincial and state permits don't all default to the same datum, and a boundary that's off by a projection error will skew your overcut figure without anyone catching it until an appeal.

If the permit includes a riparian buffer or leave strip, treat it as a second polygon, not a setback distance you eyeball later. Digitize it from the stated width (often 10 to 30 m depending on stream class) and the stream centerline in the permit package, or use the buffer polygon if the agency already generated one.

Build the as-built boundary

The as-built cut boundary comes from one of two places: a post-harvest GPS survey walked by the licensee or a field auditor, or a change-detection pass against recent imagery. A GPS walk is the traditional method and it works fine for a single disputed block, but someone has to physically trace the cutline on foot, which runs a crew day or more per block and only covers the blocks someone chose to walk.

High-resolution imagery comparison gets you the same output without the walk. A before-harvest and after-harvest image pair, run through change detection, gives the treeline as it stands this quarter.

Overlay and measure

Once both polygons sit in the same projection, load them into GIS software (QGIS and ArcGIS both handle this the same way) and run a geometric difference. Subtract the permitted boundary from the as-built boundary and what's left is the overcut polygon: the area that was cut but wasn't in the permit. Run the same difference against the riparian buffer layer separately. A block can sit inside its outer boundary and still show a buffer incursion, and agencies treat those as two separate violations with two separate thresholds.

Report overcut as area, in hectares or acres, unless the permit condition specifically calls for a percentage test. A 0.3-hectare overcut on a 4-hectare block and a 0.3-hectare overcut on a 400-hectare block are different compliance events even though they're the same number of hectares, and the hectare figure is what goes in the field order.

Where this breaks down at scale

That process is quick for one block with a disputed boundary. It gets slow once a district has to run it across every cutting permit each quarter, because the as-built boundary has to exist for a block before anyone knows whether the geometric difference is even worth running. Most compliance programs still triage that with field audits, which means the crew finds the overcut the same day they're standing in it.

A quarterly comparison of permitted boundaries against cut extent, run as change detection across a district instead of block by block, turns that triage into a desk review. The overcut list exists before anyone drives out, and the field day goes to the blocks that flagged. That's the layer Harvest Compliance builds for regulators and certifiers who need to know where to send an inspector before the season's audits start.

If your office is still finding overcut by field visit alone, it's worth checking what a remote first pass would have flagged last quarter.