Dealing with thousands of features of vector layer in OpenLayers?

Question

I am building a webgis portal too show a big number of polylines (road network) and points (villages, cities etc.). All my data are stored in a POSTGIS and throuh geoserver and Openlayers I display them on the map. For displaying I use two WFS vector layer (one for each geometry). I decided to use WFS instead of a WMS (WMSGetFeatureInfo) as this is what geoserver manual suggests here (regarding the GetFeatureInfo and GetFeature).

The problem comes when the number of features becomes relative big (around 10000 thousand features). My question is how can I deal with such a big number of features. I know one solution is BBOX but I am afraid this can slow things down by sending multiple requests.

Is there another strategy out there?

Answer 1

I will describe the way I dealed with the problem. As I mentioned before I have approximately 10000 geometries that I want to display on a map. My data are stored in a POSTGIS database and I use Geoserver (localserver) and Openlayers to display them. Also I need to interact with the data. Get attribute info for each feature and in some cased to manipulate them.

I wrote two different scripts one using WMS layers and the other using WFS layers. I run some speed tests (for the requests) using Firebug and as expected the WFS request was taking much much more. So much more that is not acceptable for my app (see screenshots WFS/WMS )

After reading the above answers and comments I decided to do the following:

• I created WMS Layers for my data
• I registered a zoom event
• After the user reaching a predifined zoom level I send a WFS request with a BBOX strategy

This is my code. I hope it helps someone else with similar issue.

<script defer="defer" type="text/javascript">
<!-- DEFINE PROXY.CGI URL -->
OpenLayers.ProxyHost = "http://localhost/cgi-bin/proxy.cgi?url=";
<!-- DEFINE GLOBAL VARIABLES -->
var map,wms, control;

<!-- DEFINE FUNCTION INIT -->
function init(){
    map = new OpenLayers.Map('map',{}); // define map 
    wms = new OpenLayers.Layer.WMS( "OpenLayers WMS","http://vmap0.tiles.osgeo.org/wms/vmap0", {layers: 'basic'} ); // define map layer


    // layer nodes
    wms_layer_komvoi = new OpenLayers.Layer.WMS( "Κόμβοι","http://localhost:8080/geoserver/wms", 
            {layers: 'rural:komvoi_real',
            transparent: true},
            {projection: new OpenLayers.Projection("EPSG:900913")});
        // layer network    
        wms_layer_network = new OpenLayers.Layer.WMS( "Ολόκληρο Δίκτυο","http://localhost:8080/geoserver/wms", 
            {layers: 'rural:foc_network',
            transparent: true},
            {projection: new OpenLayers.Projection("EPSG:900913")},
            {
            }); 

        // add layers
        map.addLayers([wms_layer_komvoi,wms_layer_network,wms]); // first you put the layer with the points
        map.zoomToExtent( new OpenLayers.Bounds(36.190737, 35.353912,35.150577, 50.274810));

        <!-- CONTROL LAYER SWITCHER -->
        map.addControl(new OpenLayers.Control.LayerSwitcher());
        <!-- REGISTER AN EVENT TO LOAD WFS VECTOR LAYERS -->
        map.events.register("zoomend", map, function(){ // event zoomend 
            zoom = map.getZoom();
            var layerNetwork = map.getLayersByName('Δίκτυο'); // check if the layer exists
            if((zoom==11) && (layerNetwork.length==0)){
                <!-- OVERLAY WFS LAYER WITH NETWORK FROM GEOSERVER BBOX STRATEGY -->
                wfs_layer_network = new OpenLayers.Layer.Vector("Δίκτυο", {
                    visibility: true,
                    //displayInLayerSwitcher: true,                     
                    strategies: [new OpenLayers.Strategy.BBOX()],
                    protocol: new OpenLayers.Protocol.WFS({
                        version: "1.1.0",
                        url: "http://localhost:8080/geoserver/wfs", 
                        featurePrefix: "rural", //workspace from geoserver
                        featureType: "foc_network", //layer name from geoserver
                        featureNS : "http://www.opengeospatial.net/rural", //namespace from geoserver
                    })
                })
                map.removeLayer(wms_layer_network);
                map.addLayer(wfs_layer_network);
            }
            if ((zoom<11) && (layerNetwork.length!==0)){
                map.removeLayer(wfs_layer_network);
                map.addLayer(wms_layer_network);
            }
        });
}// end init    
</script>   

Answer 2

You could also use WMS or even preseeded tiles and just grab the single features you need to edit from wfs.

http://dev.openlayers.org/releases/OpenLayers-2.10/examples/getfeature-wfs.html

Answer 3

With your stack, I'd suggest try to use GeoJSON as transport format but anyway, 10K are a lot of features to be handled by the client browser. I'd think on a WMS rendering for low scales and only when user is really going to do something meaningful with the data (selections probably) at larger scales then download only the vector features present on the bbox.

Also, something to take in account is the simplification of geometries for your road network according to the scale is being rendered. It all depends on your use case, interactivity on the client side, etc. You can search on this site for other questions related with vector features, lot of good answers here (definitely better than mine).