Function XPLMMapScaleMeter 

pub unsafe extern "C" fn XPLMMapScaleMeter(
    projection: XPLMMapProjectionID,
    mapX: f32,
    mapY: f32,
) -> f32

XPLMMapScaleMeter

Returns the number of map units that correspond to a distance of one meter at a given set of map coordinates.

Only valid from within a map layer callback (one of XPLMMapPrepareCacheCallback_f, XPLMMapDrawingCallback_f, XPLMMapIconDrawingCallback_f, or XPLMMapLabelDrawingCallback_f.)