Question

I’m trying to draw US state outlines with the D3 framework (http://mbostock.github.com/d3/) but am having issues generating the actual SVG data. I’ve written my code to follow the Chloropleth example (as it most closely resembles what this project needs), made sure the supplied data is in geoJSON format, and AFAIK have the backend half of this working fine.

The problem is that when I view the DOM, the <svg> object contains only one <g> element (which I created manually, per the example), and none of the child <path> elements that should under it. My code seems fairly identical to the example, and my data appears to look correct, though I am outputting MultiPolygons instead of the Polygon object that the example uses.

Our app is a RoR project with jQuery (we’re only using D3 for the SVG and geography features). The test page tries to create an <svg> element under a div called theArea, based upon the selection from a dropdown select of U.S. states:

$(document).ready( function() {

  $("#chooser_state").change( function() {

    var status = "#status";
    var statebox = "#chooser_state";
    var theArea = "#theArea"

    var url = "/test/get_state_geom";
    var data = { state: $(statebox).val() };

    $(status).text("Request sent...");

    $.post(url, jQuery.param(data), function(resp) {

      $(status).text("Received response: " + resp["message"]);
      $(theArea).empty();

      var path = d3.geo.path();
      var svg = d3.select(theArea).append("svg");
      var state = svg.append("g").attr("id", "state_view");
      var features = resp.payload.features;

      $(status).text("Created SVG object");

      state.selectAll("path")
        .data(features)
        .enter()
        .append("path")
        .attr("d", path );

    });
  });
});

The data we’re feeding D3 looks like this:

{
 'type' => 'Feature',
 'id' => '01',
 'properties' => {
                  'name' => 'Colorado'
                 },
 'geometry' => {
                'type' => 'MultiPolygon',
                'coordinates' => [
                                  [
                                   [
                                    [
                                     -106.190553863626,
                                     40.9976070173843
                                    ],
                                    [
                                     -106.061181,
                                     40.996998999999995
                                    ],
                                    < -- and so on -- >
                                   ]
                                  ]
                                 ]
               }
}

Can someone clue me in to what we’re doing wrong? I am new to geo and GIS stuff. I suspect the problem lies with the data() function, as it looks like it should be creating the blank <path> objects for each Feature (though we have only one, at the moment), but the D3 documentation seems unclear (and difficult to understand).

EDIT: Just wanted to add that the geoJSON we generate was created by the geoJSON extension for the GeoRuby gem. The actual map lines were sourced from the consolidated data that US Census Bureau’s cartographic boundary files, which were converted to SQL and saved with postGIS. Part of me suspects the geoJSON extension is doing something wrong, so that is my next avenue of attack.

Answer 1

After giving up on this and then coming back, I noticed that my FeaturesCollection was not, in fact, a collection. There’s a small detail that is easy to overlook when examining geoJSON samples: the contents of the FeaturesCollection is an array of hashes, not a single hash.