Water mask array scan order is ambiguous

"Values in the mask are defined from north-to-south, west-to-east; the first byte in the mask defines the watermask value for the northwest corner of the tile."

This doesn't make it clear whether the values are in latitude-major or longitude-major order. Either order can be interpreted as complying with that sentence. I'm guess latitude-major order, so that the north edge is traversed first?

Start with the mask-order definition quoted in the issue and determine the intended latitude-major or longitude-major traversal. Clarify the specification so the scan order is unambiguous, including which edge is traversed first; the work is done when both dimensions have only one possible interpretation.

Written by the indexing model from the issue text.