Grid Weighting of Regional Climate Model

Define objective method of determining when 'grid-weighting' (small areas, ex. City of Hamburg) vs. creation of a '0/1 mask' (large areas, ex. Germany) should be applied when selecting the 'region of interest' from the Regional Climate Model data.

See comments: https://git.geomar.de/digital-earth/de-change-backend-module/issues/3#note_15304