row-major moisture, 0..1
how many columns the coarse region grid has
coarse region id per cell, row-major; region r's cells share (y / regionSize) * cols + (x / regionSize)
each river's cells from its source to its mouth or lake
each road's cells, settlement to settlement; river crossings are the ford sites
row-major terrain ids, width * height entries
row-major elevation, 0..1, the field
terrainwas classified from