typedef void (* XPLMMapDrawingCallback_f)(
                         XPLMMapLayerID       inLayer,    
                         const float *        inMapBoundsLeftTopRightBottom,    
                         float                zoomRatio,    
                         float                mapUnitsPerUserInterfaceUnit,    
                         XPLMMapStyle         mapStyle,    
                         XPLMMapProjectionID  projection,    
                         void *               inRefcon);    

This is the OpenGL map drawing callback for plugin-created map layers. You can perform arbitrary OpenGL drawing from this callback, with one exception: changes to the Z-buffer are not permitted, and will result in map drawing errors.

All drawing done from within this callback appears beneath all built-in X-Plane icons and labels, but above the built-in “fill” layers (layers providing major details, like terrain and water). Note, however, that the relative ordering between the drawing callbacks of different plugins is not guaranteed.