The quantized-mesh watermask extension (id 2): per the spec, either a single
byte covering the whole tile, or a 256×256 row-major grid — 255 = water,
0 = land (intermediate values appear along coastlines). Rows run south →
north and columns west → east, the same orientation as the tile's u/v
(so row index maps to the v fraction, column to the u fraction).
The quantized-mesh
watermaskextension (id 2): per the spec, either a single byte covering the whole tile, or a 256×256 row-major grid —255= water,0= land (intermediate values appear along coastlines). Rows run south → north and columns west → east, the same orientation as the tile's u/v (so row index maps to thevfraction, column to theufraction).