public static SpatialReference CreateSpatialReference( 
   int wkid
)

{
  // Use a builder convenience method or use a builder constructor.

  // SpatialReferenceBuilder convenience methods don't need to run on the MCT.
  SpatialReference sr3857 = SpatialReferenceBuilder.CreateSpatialReference(3857);

  // SpatialReferenceBuilder constructors need to run on the MCT.
  ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
  {
    using (SpatialReferenceBuilder srBuilder = new SpatialReferenceBuilder(3857))
    {
      // do something with the builder

      sr3857 = srBuilder.ToSpatialReference();
    }
  });
}

{
  // create the polygon
  List<MapPoint> pts =
  [
    MapPointBuilderEx.CreateMapPoint(1.0, 1.0, SpatialReferences.WGS84),
  MapPointBuilderEx.CreateMapPoint(1.0, 2.0, SpatialReferences.WGS84),
  MapPointBuilderEx.CreateMapPoint(2.0, 2.0, SpatialReferences.WGS84),
  MapPointBuilderEx.CreateMapPoint(2.0, 1.0, SpatialReferences.WGS84),
];

  polygon = PolygonBuilderEx.CreatePolygon(pts);
  // ensure it is simple
  bool isSimple = GeometryEngine.Instance.IsSimpleAsFeature(polygon);

  // create the spatial reference to project to
  SpatialReference northPole = SpatialReferenceBuilder.CreateSpatialReference(102018);   // north pole stereographic 

  // project
  Geometry geometry = GeometryEngine.Instance.Project(polygon, northPole);
}

{
  // methods need to run on the MCT
  ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
  {
    //
    // find the first transformation used between spatial references 4267 and 4326
    //
    SpatialReference sr4267 =
         SpatialReferenceBuilder.CreateSpatialReference(4267);
    SpatialReference sr4326 = SpatialReferences.WGS84;

    List<ProjectionTransformation> transformations =
           ProjectionTransformation.FindTransformations(sr4267, sr4326);
    // transformations.Count = 1
    ProjectionTransformation projTrans = transformations[0];
    CompositeGeographicTransformation compositeGT =
         projTrans.Transformation as CompositeGeographicTransformation;
    GeographicTransformation gt = compositeGT[0];
    // gt.Wkid = 15851
    // gt.Name = "NAD_1927_To_WGS_1984_79_CONUS"
    // gt.IsForward = true


    //
    // find the first five transformation used between spatial references 4267 and 4326
    //
    transformations = ProjectionTransformation.FindTransformations(
                                       sr4267, sr4326, numResults: 5);
    // transformations.Count = 5
    projTrans = transformations[0];
    compositeGT = projTrans.Transformation as CompositeGeographicTransformation;
    // compositeGT.Count = 1
    // compositeGT[0].Wkid = 15851
    // compositeGT[0].Name = "NAD_1927_To_WGS_1984_79_CONUS"
    // compositeGT[0].IsForward = true

    projTrans = transformations[1];
    compositeGT = projTrans.Transformation as CompositeGeographicTransformation;
    // compositeGT.Count = 1
    // compositeGT[0].Wkid = 1173
    // compositeGT[0].Name = "NAD_1927_To_WGS_1984_4"
    // compositeGT[0].IsForward = true

    projTrans = transformations[2];
    compositeGT = projTrans.Transformation as CompositeGeographicTransformation;
    // compositeGT.Count = 1
    // compositeGT[0].Wkid = 1172
    // compositeGT[0].Name = "NAD_1927_To_WGS_1984_3"
    // compositeGT[0].IsForward = true

    projTrans = transformations[3];
    compositeGT = projTrans.Transformation as CompositeGeographicTransformation;
    // compositeGT.Count = 2
    // compositeGT[0].Wkid = 1241
    // compositeGT[0].Name = "NAD_1927_To_NAD_1983_NADCON"
    // compositeGT[0].IsForward = true

    // compositeGT[1].Wkid = 108190
    // compositeGT[1].Name = "WGS_1984_(ITRF00)_To_NAD_1983"
    // compositeGT[1].IsForward = false

    projTrans = transformations[4];
    compositeGT = projTrans.Transformation as CompositeGeographicTransformation;
    // compositeGT.Count = 2
    // compositeGT[0].Wkid = 1241
    // compositeGT[0].Name = "NAD_1927_To_NAD_1983_NADCON"
    // compositeGT[0].IsForward = true

    // compositeGT[1].Wkid = 1515
    // compositeGT[1].Name = "NAD_1983_To_WGS_1984_5"
    // compositeGT[1].IsForward = true


    //
    // find the first transformation used between spatial
    // references 4267 and 4326 within Alaska
    //

    // Alaska
    Envelope envelope = EnvelopeBuilderEx.CreateEnvelope(-161, 61, -145, 69);
    transformations = ProjectionTransformation.FindTransformations(
                                                sr4267, sr4326, envelope);
    // transformations.Count = 1
    projTrans = transformations[0];
    compositeGT = projTrans.Transformation as CompositeGeographicTransformation;
    // compositeGT.Count = 2
    // compositeGT[0].Wkid = 1243
    // compositeGT[0].Name = "NAD_1927_To_NAD_1983_Alaska"
    // compositeGT[0].IsForward = true

    // compositeGT[1].Wkid = 108190
    // compositeGT[1].Name = "WGS_1984_(ITRF00)_To_NAD_1983"
    // compositeGT[1].IsForward = false


    //
    // find the first geographic transformation used between two spatial references with VCS  (use vertical = false)
    //
    SpatialReference inSR =
                    SpatialReferenceBuilder.CreateSpatialReference(4269, 115702);
    SpatialReference outSR =
                    SpatialReferenceBuilder.CreateSpatialReference(4326, 3855);

    // Even though each spatial reference has a VCS,
    // vertical = false should return geographic transformations.
    transformations = ProjectionTransformation.FindTransformations(inSR, outSR);
    // transformations.Count = 1
    projTrans = transformations[0];
    compositeGT = projTrans.Transformation as CompositeGeographicTransformation;
    // compositeGT.Count = 1
    // compositeGT[0].Wkid = 108190
    // compositeGT[0].Name = ""WGS_1984_(ITRF00)_To_NAD_1983"
    // compositeGT[0].IsForward = false

    //
    // find the first vertical transformation used between two spatial references with VCS  (use vertical = true)
    //

    transformations =
              ProjectionTransformation.FindTransformations(
                                      inSR, outSR, vertical: true);
    // transformations.Count = 1
    projTrans = transformations[0];

    CompositeHVDatumTransformation compositeHV =
            projTrans.Transformation as CompositeHVDatumTransformation;
    // compositeHV.Count = 2
    // compositeHV[0].Wkid = 1188
    // compositeHV[0].Name = "NAD_1983_To_WGS_1984_1"
    // compositeHV[0].IsForward = true

    // compositeHV[1].Wkid = 110019
    // compositeHV[1].Name = "WGS_1984_To_WGS_1984_EGM2008_2.5x2.5_Height"
    // compositeHV[1].IsForward = true
  });
}