Shared standard As Double

Protected Sub Page_Load(sender As Object, e As EventArgs)
	If Not Page.IsPostBack Then
		Map1.MapBackground.BackgroundBrush = New GeoSolidBrush(GeoColor.FromHtml("#E5E3DF"))
		Map1.CurrentExtent = New RectangleShape(-125, 72, 50, -46)
		Map1.MapUnit = GeographyUnit.DecimalDegree

		Dim worldMapKitOverlay As New WorldMapKitWmsWebOverlay()
		Map1.CustomOverlays.Add(worldMapKitOverlay)

		Dim worldLayer As New ShapeFileFeatureLayer(MapPath("~/SampleData/world/cntry02.shp"))
		worldLayer.Open()
		worldLayer.ZoomLevelSet.ZoomLevel01.ApplyUntilZoomLevel = ApplyUntilZoomLevel.Level20
		worldLayer.ZoomLevelSet.ZoomLevel01.DefaultAreaStyle = AreaStyles.CreateSimpleAreaStyle(GeoColor.SimpleColors.Blue, GeoColor.FromArgb(100, GeoColor.SimpleColors.Green))
		worldLayer.ZoomLevelSet.ZoomLevel01.DefaultAreaStyle.RequiredColumnNames.Add("POP_CNTRY")
		AddHandler worldLayer.DrawingFeatures, AddressOf worldLayer_DrawingFeatures

		Dim staticOverlay As New LayerOverlay()
		staticOverlay.IsBaseOverlay = False
		staticOverlay.Layers.Add(worldLayer)
		Map1.CustomOverlays.Add(staticOverlay)

		standard = 100000000
	End If
End Sub

Private Sub worldLayer_DrawingFeatures(sender As Object, e As DrawingFeaturesEventArgs)
	Dim newFeatures As New Collection(Of Feature)()
	For Each item As var In e.FeaturesToDraw
		Dim pop As Double = Double.Parse(item.ColumnValues("POP_CNTRY"))
		If pop > standard Then
			newFeatures.Add(item)
		End If
	Next

	e.FeaturesToDraw.Clear()

	For Each item As var In newFeatures
		e.FeaturesToDraw.Add(item)
	Next

End Sub

Protected Sub Button1_Click(sender As Object, e As EventArgs)
	standard = 1000000000
	' do your logic
End Sub