showed map coordinate

how to check if the added/selected marker is outside the area displayed on the map

First use the TMSFNCMaps.GetBounds call to retrieve the current displayed area of the map in the OnGetBounds event.

Then you can use the IsPointInArea to check if the marker coordinate is inside the bounds of the map. https://download.tmssoftware.com/doc/tmsfncmaps/components/ttmsfncmaps/#common-types