/// <summary>
        /// Initializes labels tab
        /// </summary>
        private void InitLabelsTab()
        {
            MapWinGIS.Labels lb = _shapefile.Labels;
            chkShowLabels.Checked = lb.Visible;

            chkLabelFrame.Checked = lb.FrameVisible;
            clpLabelFrame.Color   = Colors.UintToColor(lb.FrameBackColor);
            udLabelFontSize.SetValue(lb.FontSize);
        }
        /// <summary>
        /// Sets the properties of the labels based upon user input
        /// </summary>
        private void UpdateLabels()
        {
            MapWinGIS.Labels lb = _shapefile.Labels;
            lb.Visible = chkShowLabels.Checked;

            // categories will have the same alignment
            for (int i = 0; i < _shapefile.Labels.NumCategories; i++)
            {
                MapWinGIS.LabelCategory cat = _shapefile.Labels.get_Category(i);
                cat.Alignment = lb.Alignment;
                cat.OffsetX   = lb.OffsetX;
                cat.OffsetY   = lb.OffsetY;
            }

            DrawLabelsPreview();
        }