The usage is consistent with, for example
CountryData[Entity["Country", "UnitedKingdom"], "Coordinates"]
which can then be used in a Graphics like this
Graphics[{Line[
CountryData[Entity["Country", "UnitedKingdom"], "Coordinates"]]}]
or
Graphics[{Polygon[
CountryData[Entity["Country", "UnitedKingdom"], "Coordinates"]]}]
or more usefully by inserting a GeoPosition into a GeoGraphics as in this
GeoGraphics[{GeoPosition[
CountryData[Entity["Country", "UnitedKingdom"], "Coordinates"]]}]