protected void ProcessButton_Click(object sender, EventArgs e)
        {
            // build data
            int maxItems = AlwaysConvert.ToInt(list_TopCount.SelectedValue, 10);
            IList <SalesByProvinceSummary> rptData = ReportDataSource.GetSalesByState(list_Country.SelectedValue, StartDate.SelectedDate, EndDate.SelectedDate, maxItems, 0, "TotalSales DESC");

            Chart1.Visible = rptData.Count > 0;
            BuildCharts(rptData);
        }