ArcGIS Pro 2.7 API Reference Guide
GetExteriorRing Method
Example 

ArcGIS.Core.Geometry Namespace > Polygon Class : GetExteriorRing Method
The index of the exterior ring. Note that this is not the index of the part in the polygon. Use ExteriorRingCount to determine the number of exterior rings in this polygon.
(Optional) Determines if the spatial reference should be set in each of the returned polygons. If setSpatialReference is set to true, then the spatial reference in each polygon is inherited from this polygon. If setSpatialReference is set to false, then the spatial reference in each polygon is set to null. The default value is true.
Gets the specified exterior ring in this polygon.
Syntax
public Polygon GetExteriorRing( 
   int index,
   bool setSpatialReference
)
Public Function GetExteriorRing( _
   ByVal index As Integer, _
   Optional ByVal setSpatialReference As Boolean _
) As Polygon

Parameters

index
The index of the exterior ring. Note that this is not the index of the part in the polygon. Use ExteriorRingCount to determine the number of exterior rings in this polygon.
setSpatialReference
(Optional) Determines if the spatial reference should be set in each of the returned polygons. If setSpatialReference is set to true, then the spatial reference in each polygon is inherited from this polygon. If setSpatialReference is set to false, then the spatial reference in each polygon is set to null. The default value is true.

Return Value

A polygon representing the exterior ring.
Exceptions
ExceptionDescription
The index is negative or is greater than or equal to the number of external rings in this polygon.
Remarks
An exterior ring is a part that is oriented clockwise.
Example
public void GetExteriorRings(Polygon inputPolygon)
{
  if (inputPolygon == null || inputPolygon.IsEmpty)
    return;

  // polygon part count
  int partCount = inputPolygon.PartCount;
  // polygon exterior ring count
  int numExtRings = inputPolygon.ExteriorRingCount;
  // get set of exterior rings for the polygon
  IList<Polygon> extRings = inputPolygon.GetExteriorRings();

  // test each part for "exterior ring"
  for (int idx = 0; idx < partCount; idx++)
  {
    bool isExteriorRing = inputPolygon.IsExteriorRing(idx);
  }
}
Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

Polygon Class
Polygon Members