utilizes Mike Bostock's excellent instructions to use D3 to render GeoJSON features on a Leaflet Map

logic is wrapped into an object that extends Leaflet's own GeoJSON layer, so its easy to add to a map using Leaflet's usual pattern:

var d3Layer = new L.GeoJSON.d3({...insert geojson here...}, options);
var map = new L.Map("map").addLayer(d3Layer);

L.GeoJSON.d3.async allows you to create a layer that references a geojson data service, such as a WFS provided by Geoserver.

var asyncD3Layer = new L.GeoJSON.d3.async("http:/url/for/geoserver/wfs");
var map = new L.Map("map").addLayer(asyncD3Layer)

• classed - Objects applied using d3's classed function.

Specifying a classed object in the options

var d3Layer = new L.GeoJSON.d3(geoJson, {
  classed: {
    feature: true,
    selected: function(d,i) { return d.properties.selected; }
  }
});

is the equivalent of performing the following options on the paths directly.

d3.classed('feature', true);
d3.classed('selected', function(d,i) { return d.properties.selected; })

• attr - Objects applied using the attr function. Useful for setting properties that have no CSS equivalent. See above for use.
• on - Objects applied using the on function. Useful for setting event listeners. See above for use.
• idFunction - If your GeoJSON data has several features you need a unique identifier for each one. By default leaflet-d3-layer will look for an id field at the root of your feature. Use this option if your features have some other unique identifier.

Example: your feature has an identifier field in the properties member.

geoJson = {
  "type": "Feature",
  "geometry": {
    "type": "Point",
    "coordinates": [125.6, 10.1]
  },
  "properties": {
    "name": "Dinagat Islands",
    "identifier": "point-dinagat"
  }
}

You would then use the idFunction option like so:

var d3Layer = new L.GeoJSON.d3(geoJson, {
  idFunction: function(d) { return d.properties.identifier; }
});

check out /dist/index.html

• there is definitely a better way to handle adding / removing data from the map using (D3's update patterns)[http://bl.ocks.org/mbostock/3808218]
• is this a good way to handle unique-value symbology? SOLVED - use idFunction option
• probably "async" layer should be branded and focused for what it is: a connector to a Geoserver WFS, although it would work right now for any GeoJSON data service that accepts a bbox query paramter