public void SetGridSpacing( 
   double spacing,
   LinearUnit spacingUnit
)

{
    var center_pt = MapView.Active.Extent.Center;
    var width = MapView.Active.Extent.Width;
    var height = MapView.Active.Extent.Height;
    var qtr_width = width * 0.25;
    var qtr_ht = height * 0.25;

    QueuedTask.Run(() =>
    {
        //use defaults
        var gridOptions = GridOptionsEnvironment.Instance.DefaultGridOptions;

        //customize the options as needed
        gridOptions.RotateWithMap = !gridOptions.RotateWithMap;
        gridOptions.GridLineColor = ColorFactory.Instance.RedRGB;

        var gs_rotation = gridOptions.GetGridRotation();
        gridOptions.SetGridRotation(gs_rotation * 1.5);

        var gs_meters = gridOptions.GetGridSpacingMeters();
        var gs_in_spacing_units = gridOptions.GetGridSpacing();
        var gs_units = gridOptions.GridSpacingUnits;

        //meters assumed
        gridOptions.SetGridSpacingInMeters(gs_meters + 10);
        //specify units explicitly
        gridOptions.SetGridSpacing(1000, LinearUnit.Feet);//internally will be converted to meters

        gridOptions.IsGridLines = true;//use lines (default)

        var grid_interval = gridOptions.GridMajorInterval;

        gridOptions.SnapToGridEnabled = true;

        var x1 = center_pt.X - qtr_width;
        var y1 = center_pt.Y + qtr_ht;
        gridOptions.SetGridOrigin(new Coordinate2D(x1, y1));
        //To apply changes, the gridoptions must be set back on the map
        GridOptionsEnvironment.Instance.SetGridOptions(map, gridOptions);
    });
}