public IPolyline TestGeometryEnvironment()
...{
    ISpatialReferenceFactory spatialReferenceFactory = new SpatialReferenceEnvironmentClass();

    //Create a projected coordinate system and define its domain, resolution, and x,y tolerance.
    ISpatialReferenceResolution spatialReferenceResolution = spatialReferenceFactory.CreateProjectedCoordinateSystem((int)esriSRProjCSType.esriSRProjCS_NAD1983UTM_11N) as ISpatialReferenceResolution;
    spatialReferenceResolution.ConstructFromHorizon();
    ISpatialReferenceTolerance spatialReferenceTolerance = spatialReferenceResolution as ISpatialReferenceTolerance;
    spatialReferenceTolerance.SetDefaultXYTolerance();
    ISpatialReference spatialReference = spatialReferenceResolution as ISpatialReference;

    //Create an array of WKSPoint structures starting in the middle of the x,y domain of the
    //projected coordinate system.

    double xMin;
    double xMax;
    double yMin;
    double yMax;
    spatialReference.GetDomain(out xMin, out xMax, out yMin, out yMax);

    double xFactor = (xMin + xMax) * 0.5;
    double yFactor = (yMin + yMax) * 0.5;

    WKSPoint[] wksPoints = new WKSPoint[10];
    for (int i = 0; i < wksPoints.Length; i++)
    ...{
        wksPoints[i].X = xFactor + i;
        wksPoints[i].Y = yFactor + i;
    }

    IPointCollection4 pointCollection = new PolylineClass();

    IGeometryBridge2 geometryBridge = new GeometryEnvironmentClass();
    geometryBridge.AddWKSPoints(pointCollection, ref wksPoints);

    IPolyline polyline = pointCollection as IPolyline;
    polyline.SpatialReference = spatialReference;

    return polyline;
}