ArcGIS Pro 2.7 API Reference Guide
Area Property (Polygon)
Example 

ArcGIS.Core.Geometry Namespace > Polygon Class : Area Property
Gets the area of this instance.
Syntax
public override double Area {get;}
Public Overrides NotOverridable ReadOnly Property Area As Double
Example
List<Coordinate2D> outerCoordinates = new List<Coordinate2D>();
outerCoordinates.Add(new Coordinate2D(10.0, 10.0));
outerCoordinates.Add(new Coordinate2D(10.0, 20.0));
outerCoordinates.Add(new Coordinate2D(20.0, 20.0));
outerCoordinates.Add(new Coordinate2D(20.0, 10.0));

// Builder constructors need to run on the MCT.
ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
{
  // use the PolygonBuilder as we wish to manipulate the parts
  using (PolygonBuilder pb = new PolygonBuilder(outerCoordinates))
  {
    Polygon donut = pb.ToGeometry();
    double area = donut.Area;       // area = 100

    // define the inner polygon as anti-clockwise
    List<Coordinate2D> innerCoordinates = new List<Coordinate2D>();
    innerCoordinates.Add(new Coordinate2D(13.0, 13.0));
    innerCoordinates.Add(new Coordinate2D(17.0, 13.0));
    innerCoordinates.Add(new Coordinate2D(17.0, 17.0));
    innerCoordinates.Add(new Coordinate2D(13.0, 17.0));

    pb.AddPart(innerCoordinates);
    donut = pb.ToGeometry();

    area = donut.Area;    // area = 84.0

    area = GeometryEngine.Instance.Area(donut);    // area = 84.0
  }
});
Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

Polygon Class
Polygon Members