New Post: When I add many markers >250 from a SQL DB , the map becomes unresponsive. -Why ?

Dim lat AsString = NothingDim lng AsString = NothingDim layer_name AsString = NothingDim info_1 AsString = NothingDim info_2 AsString = NothingDim mimage AsString = Nothing
     
        GMap1.HoldInvalidation = TrueTry
            OBJCONN.Close() : OBJCONN.Open()
            Dim Q AsNew SqlCommand("SELECT * FROM LAYERS WHERE LAYER_NAME='"& L & "'", OBJCONN)
           
            

            Dim req As System.Net.WebRequest = System.Net.WebRequest.Create("http://expressen.se/img/MapIcons/Events/Natural disaster/flood.png")
            Dim response As System.Net.WebResponse = req.GetResponse()
            Dim stream As Stream = response.GetResponseStream()
            Dim imgX As System.Drawing.Image = System.Drawing.Image.FromStream(stream)
            stream.Close()

            Dim R As SqlDataReader = Q.ExecuteReader
            While R.Read
                lat = R("LATITUDE").ToString
                lng = R("LONGITUDE").ToString()
                layer_name = R("Layer_name").ToString()
                info_1 = R("info_1").ToString()
                info_2 = R("info_2").ToString()
                mimage = R("MAP_MARKER_IMAGE")
                Dim m = New GMapMarkerImage(New PointLatLng(lat, lng), New Bitmap(imgX))
                Layer_GPSmarker.Markers.Add(m)
                m.ToolTipMode = MarkerTooltipMode.OnMouseOver
                m.ToolTipText = layer_name & vbCrLf & info_1 & vbCrLf & info_2
                GMap1.Overlays.Add(Layer_GPSmarker)

            EndWhile
            R.Close()
            OBJCONN.Close()
            GMap1.Refresh()

        Catch'FelhanteringEndTryEndSub