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 polylineFromPointList = 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 = PolylineBuilderEx.CreatePolyline(
              coords, SpatialReferences.WGS84);

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

  // export and import
  byte[] buffer = GeometryEngine.Instance.ExportToWKB(wkbExportFlags, polyline);
  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);
}