NUMPOINTS() — Returns the number of points within a polygon GEOGRAPHY value.
NUMPOINTS( polygon )
The NUMPOINTS() function returns the total number of points that comprise a polygon GEOGRAPHY value. The number of points includes the points from both the outer polygon and any inner polygons. It also includes all of the points defining the polygon. Which means the starting point for each polygon is counted twice — once as the starting point and once and the ending point — because this is required in the WKT representation of a polygon.