ArcGIS Pro 2.7 API Reference Guide
Union(IEnumerable<Geometry>) Method
Example 

ArcGIS.Core.Geometry Namespace > IGeometryEngine Interface > Union Method : Union(IEnumerable<Geometry>) Method
The collection of geometries to union.
Constructs the set-theoretic union of the input geometries.
Syntax

Parameters

geometries
The collection of geometries to union.

Return Value

A geometry representing the union of the input geometries.
Exceptions
ExceptionDescription
Geometries is null or empty.
The method is not implemented for GeometryBag.
Geometry is the wrong type for this operation. Cannot union different geometry types.
Incompatible spatial references between the input geometries.
One of the geometries has a spatial reference which is an image coordinate system.
Remarks
An exception is thrown if the SpatialReferences of the geometries are not equal or if the geometry types are not equal. However, points and multipoints are considered to be the same type.

GeometryEngine Union

Example
// union many polylines

List<Coordinate2D> coords = new List<Coordinate2D>()
{
  new Coordinate2D(1, 2), new Coordinate2D(3, 4), new Coordinate2D(4, 2),
  new Coordinate2D(5, 6), new Coordinate2D(7, 8), new Coordinate2D(8, 4),
  new Coordinate2D(9, 10), new Coordinate2D(11, 12), new Coordinate2D(12, 8),
  new Coordinate2D(10, 8), new Coordinate2D(12, 12), new Coordinate2D(14, 10)
};

// create Disjoint lines
List<Polyline> manyLines = new List<Polyline>
{
  PolylineBuilder.CreatePolyline(new List<Coordinate2D>(){coords[0], coords[1], coords[2]}, SpatialReferences.WGS84),
  PolylineBuilder.CreatePolyline(new List<Coordinate2D>(){coords[3], coords[4], coords[5]}),
  PolylineBuilder.CreatePolyline(new List<Coordinate2D>(){coords[6], coords[7], coords[8]})
};

Polyline polyline = GeometryEngine.Instance.Union(manyLines) as Polyline;
// union many polygons

List<Coordinate3D> coordsZ = new List<Coordinate3D>()
{
  new Coordinate3D(1, 2, 0), new Coordinate3D(3, 4, 1), new Coordinate3D(4, 2, 2),
  new Coordinate3D(5, 6, 3), new Coordinate3D(7, 8, 4), new Coordinate3D(8, 4, 5),
  new Coordinate3D(9, 10, 6), new Coordinate3D(11, 12, 7), new Coordinate3D(12, 8, 8),
  new Coordinate3D(10, 8, 9), new Coordinate3D(12, 12, 10), new Coordinate3D(14, 10, 11)
};

// create polygons
List<Polygon> manyPolygonsZ = new List<Polygon>
{
  PolygonBuilder.CreatePolygon(new List<Coordinate3D>(){coordsZ[0], coordsZ[1], coordsZ[2]}, SpatialReferences.WGS84),
  PolygonBuilder.CreatePolygon(new List<Coordinate3D>(){coordsZ[3], coordsZ[4], coordsZ[5]}),
  PolygonBuilder.CreatePolygon(new List<Coordinate3D>(){coordsZ[6], coordsZ[7], coordsZ[8]})
};

Polygon polygon = GeometryEngine.Instance.Union(manyPolygonsZ) as Polygon;
Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

IGeometryEngine Interface
IGeometryEngine Members
Overload List