ArcGIS Pro 2.7 API Reference Guide
Area Method (IGeometryEngine)
Example 

ArcGIS.Core.Geometry Namespace > IGeometryEngine Interface : Area Method
The geometry of which the area will be calculated.
Gets the area of the geometry. This is a planar measurement using 2D Cartesian mathematics to compute the area.
Syntax
Function Area( _
   ByVal geometry As Geometry _
) As Double

Parameters

geometry
The geometry of which the area will be calculated.

Return Value

The computed area in the same units as the geometry's spatial reference unit.
Exceptions
ExceptionDescription
Geometry is null or empty.
The method is not implemented for GeometryBag.
Example
var g1 = PolygonBuilder.FromJson("{\"rings\": [ [ [0, 0], [10, 0], [10, 10], [0, 10] ] ] }");
double d = GeometryEngine.Instance.Area(g1);
// d = -100.0         //negative due to wrong ring orientation
d = GeometryEngine.Instance.Area(GeometryEngine.Instance.SimplifyAsFeature(g1));
// d = 100.0        // feature has been simplifed; ring orientation is correct
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

IGeometryEngine Interface
IGeometryEngine Members