Indicates the type of map layer you are creating. Fill layers will always be drawn beneath markings layers.

xplm_MapLayer_Fill"0" A layer that draws "fill" graphics, like weather patterns, terrain, etc. Fill layers frequently cover a large portion of the visible map area.
xplm_MapLayer_Markings"1" A layer that provides markings for particular map features, like NAVAIDs, airports, etc. Even dense markings layers cover a small portion of the total map area.