footprint-field

footprint3d — edit a province's footprint as the shape it is. A polygon drawn inside a square, vertices you drag where they actually are. The rules live in curve.ts; this is the view.

Why not the curve view

A footprint can be edited as extent-against-angle on a graph, and it is miserable: a hexagon looks like a wave, and moving a corner means finding which bump is that corner. Tonio: "the footprint would work MUCH better as a radial editor. A hexagon would just be a hexagon."

The square is the province's bounds, so the picture answers "how much of my extent am I using, and in which directions" without being read.

Six numbers for a hexagon

The polygon is its vertices — no sampling. That works because polygonExtent casts a ray at the real straight edge instead of interpolating radius against angle, which bows every edge inward. A circle is therefore the expensive shape: there is no finite polygon that is one, so it is a 16-gon, indistinguishable at province scale for sixteen numbers.

Two rules, both clamps

A vertex cannot pass its neighbours (angles stay monotonic) and cannot reach the centre. Together those keep the polygon star-shaped about its centre, which is what makes "extent in this direction" have an answer at all. Both are clamps rather than refusals — a drag that stops at the limit shows you the limit; one that refuses to move looks broken.