Curves on a square grid
A mathematical circle contains infinitely many points, but a block plan must choose whole grid cells. Rasterization decides which cells best approximate the boundary.
Symmetry and deterministic output
Blockform evaluates pixel centers against an ellipse boundary, applies the same rule in every quadrant, and subtracts inward layers for outline thickness. Identical settings therefore produce identical plans.
Runs are build instructions
Adjacent selected cells form a run. The row plan exposes those runs so builders can count straight sections rather than interpret a picture.