public static SpatialReference WGS84 {get;}

SpatialReference wgs84 = SpatialReferences.WGS84;
bool isProjected = wgs84.IsProjected;     // false
bool isGeographic = wgs84.IsGeographic;   // true

// Get datum of a spatial reference
SpatialReference srWgs84 = SpatialReferences.WGS84;
Datum datum = srWgs84.Datum;
// datum.Name = "D_WGS_1984"
// datum.Wkid = 6326
// datum.SpheroidName = "WGS_1984"
// datum.SpheroidWkid = 7030
// datum.SpheroidFlattening = 0.0033528106647474805
// datum.SpheroidSemiMajorAxis = 6378137.0
// datum.SpheroidSemiMinorAxis = 6356752.3142451793

// Custom WKT
string wyomingWkt = "PROJCS[\"Wyoming_State_Pl_NAD_1927\",GEOGCS[\"GCS_North_American_1927\",DATUM[\"D_North_American_1927_Perry\",SPHEROID[\"Clarke_1866_Chase\",6378210.0,250.0]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]],PROJECTION[\"Transverse_Mercator\"],PARAMETER[\"false_easting\",500000.0],PARAMETER[\"false_northing\",0.0],PARAMETER[\"central_meridian\",-107.3333333],PARAMETER[\"scale_factor\",0.9999412],PARAMETER[\"latitude_of_origin\",40.66666667],UNIT[\"Foot_US\",0.3048006096012192]]";
SpatialReference srFromWkt = SpatialReferenceBuilder.CreateSpatialReference(wyomingWkt);
datum = srWgs84.Datum;
// datum.Name = "D_North_American_1927_Perry"
// datum.Wkid = 0
// datum.SpheroidName = "Clarke_1866_Chase"
// datum.SpheroidWkid = 0
// datum.SpheroidFlattening = 0.004
// datum.SpheroidSemiMajorAxis = 6378210.0
// datum.SpheroidSemiMinorAxis = 6352697.16

// Use a builderEx convenience method or a builderEx constructor.
// neither need to run on the MCT

MapPoint startPt = MapPointBuilderEx.CreateMapPoint(1.0, 1.0);
MapPoint endPt = MapPointBuilderEx.CreateMapPoint(2.0, 1.0);

List<MapPoint> list = new List<MapPoint>() { startPt, endPt };

Polyline polyline = PolylineBuilderEx.CreatePolyline(list, SpatialReferences.WGS84);

// use AttributeFlags.None since we only have 2D points in the list
PolylineBuilderEx pb = new PolylineBuilderEx(list, AttributeFlags.None);
pb.SpatialReference = SpatialReferences.WGS84;
Polyline polyline2 = pb.ToGeometry();

// Use AttributeFlags.NoAttributes because we only have 2d points in the list
Polyline polyline4 = PolylineBuilderEx.CreatePolyline(list, AttributeFlags.None);

// create a polyline
List<Coordinate2D> coords = new List<Coordinate2D>
{
  new Coordinate2D(0, 0),
  new Coordinate2D(0, 1),
  new Coordinate2D(1, 1),
  new Coordinate2D(1, 0)
};

Polyline polyline = PolylineBuilderEx.CreatePolyline(
            coords, SpatialReferences.WGS84);

WkbExportFlags wkbExportFlags = WkbExportFlags.WkbExportDefaults;
WkbImportFlags wkbImportFlags = WkbImportFlags.WkbImportDefaults;

// export and import
byte[] buffer = GeometryEngine.Instance.ExportToWKB(wkbExportFlags, polyline);
Geometry geometry = GeometryEngine.Instance.ImportFromWKB(
               wkbImportFlags, buffer, SpatialReferences.WGS84);
Polyline importPolyline = geometry as Polyline;


// alternatively, determine the size for the buffer
int bufferSize = GeometryEngine.Instance.GetWKBSize(wkbExportFlags, polyline);
buffer = new byte[bufferSize];
// export
bufferSize = GeometryEngine.Instance.ExportToWKB(
                wkbExportFlags, polyline, ref buffer);
// import
importPolyline = GeometryEngine.Instance.ImportFromWKB(
         wkbImportFlags, buffer, SpatialReferences.WGS84) as Polyline;

// create an envelope
List<MapPoint> coordsZM = new List<MapPoint>
{
  MapPointBuilderEx.CreateMapPoint(1001, 1002, 1003, 1004),
  MapPointBuilderEx.CreateMapPoint(2001, 2002, Double.NaN, 2004),
  MapPointBuilderEx.CreateMapPoint(3001, -3002, 3003, 3004),
  MapPointBuilderEx.CreateMapPoint(1001, -4002, 4003, 4004)
};

Envelope envelope = EnvelopeBuilderEx.CreateEnvelope(
           coordsZM[0], coordsZM[2], SpatialReferences.WGS84);

// export and import
EsriShapeExportFlags exportFlags = EsriShapeExportFlags.EsriShapeExportDefaults;
EsriShapeImportFlags importFlags = EsriShapeImportFlags.EsriShapeImportDefaults;
byte[] buffer = GeometryEngine.Instance.ExportToEsriShape(exportFlags, envelope);
Polygon importedPolygon = GeometryEngine.Instance.ImportFromEsriShape(
               importFlags, buffer, envelope.SpatialReference) as Polygon;
Envelope importedEnvelope = importedPolygon.Extent;

// export without z,m
buffer = GeometryEngine.Instance.ExportToEsriShape(
        EsriShapeExportFlags.EsriShapeExportStripZs | 
        EsriShapeExportFlags.EsriShapeExportStripMs, envelope);
importedPolygon = GeometryEngine.Instance.ImportFromEsriShape(
        importFlags, buffer, SpatialReferences.WGS84) as Polygon;
importedEnvelope = importedPolygon.Extent;

bool hasZ = importedEnvelope.HasZ;      // hasZ = false
bool hasM = importedEnvelope.HasM;      // hasM = false

// export with shapeSize
int bufferSize = GeometryEngine.Instance.GetEsriShapeSize(
                                       exportFlags, envelope);
buffer = new byte[bufferSize];

bufferSize = GeometryEngine.Instance.ExportToEsriShape(
                             exportFlags, envelope, ref buffer);
importedPolygon = GeometryEngine.Instance.ImportFromEsriShape(
                    importFlags, buffer, envelope.SpatialReference) as Polygon;
importedEnvelope = importedPolygon.Extent;


// or use the envelope and envelopeBuilderEx classes
buffer = envelope.ToEsriShape();
// buffer represents a polygon as there is not an envelope Esri shape buffer
// EnvelopeBuilderEx.FromEsriShape takes a polygon Esri shape buffer and returns the extent of the polygon.
importedEnvelope = EnvelopeBuilderEx.FromEsriShape(buffer);