How to import into Unity
Easiest path — hit Save .zip, unzip anywhere under Assets, drop
HeightfieldImporter.cs into an Editor folder, then run
Tools → Heightfield Importer → Import grid. It builds the terrain(s), colours them,
and places your markers & roads. Manual path: Terrain → Terrain Settings →
Import Raw… (Depth Bit 16, Byte Order Windows, tick Flip Vertically if mirrored).
Splatmap channels: R grass · G rock · B snow · A sand.