A demo of TopoJSON on a U.S. counties shapefile from the U.S. census bureau. The original GeoJSON file was 2.2M; the TopoJSON file is 660K, a reduction of 70.5%! (Or gzipped, a 71% reduction from 596K to 176K.)
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U.S. Counties TopoJSON
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| <!DOCTYPE html> | |
| <meta charset="utf-8"> | |
| <style> | |
| .stroke { | |
| fill: none; | |
| stroke: #000; | |
| stroke-width: .5px; | |
| } | |
| </style> | |
| <body> | |
| <script src="http://d3js.org/d3.v3.js"></script> | |
| <script src="topojson.js"></script> | |
| <script> | |
| var width = 960, | |
| height = 500; | |
| var color = d3.scale.category20c(); | |
| var path = d3.geo.path(); | |
| var svg = d3.select("body").append("svg") | |
| .attr("width", width) | |
| .attr("height", height); | |
| d3.json("../4090846/us-counties.json", function(error, topology) { | |
| svg.selectAll("path") | |
| .data(topojson.object(topology, topology.objects[0]).geometries) | |
| .enter().append("path") | |
| .attr("d", path) | |
| .style("fill", function(d) { return color(d.id / 1000 | 0); }) | |
| .style("fill-opacity", function(d) { return ((d.id % 6) + 6) / 12; }); | |
| svg.append("path") | |
| .datum(topojson.mesh(topology)) | |
| .attr("class", "stroke") | |
| .attr("d", path); | |
| }); | |
| </script> |
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| topojson = (function() { | |
| function mesh(topology) { | |
| var arcs = [], i = -1, n = topology.arcs.length; | |
| while (++i < n) arcs.push([i]); | |
| return object(topology, {type: "MultiLineString", arcs: arcs}); | |
| } | |
| function object(topology, o) { | |
| var tf = topology.transform, | |
| kx = tf.scale[0], | |
| ky = tf.scale[1], | |
| dx = tf.translate[0], | |
| dy = tf.translate[1], | |
| arcs = topology.arcs; | |
| function arc(i, points) { | |
| if (points.length) points.pop(); | |
| for (var a = arcs[i < 0 ? ~i : i], k = 0, n = a.length, x = 0, y = 0, p; k < n; ++k) points.push([ | |
| (x += (p = a[k])[0]) * kx + dx, | |
| (y += p[1]) * ky + dy | |
| ]); | |
| if (i < 0) reverse(points, n); | |
| } | |
| function line(arcs) { | |
| var points = []; | |
| for (var i = 0, n = arcs.length; i < n; ++i) arc(arcs[i], points); | |
| return points; | |
| } | |
| function polygon(arcs) { | |
| return arcs.map(line); | |
| } | |
| function geometry(o) { | |
| o = Object.create(o); | |
| o.coordinates = geometryType[o.type](o.arcs); | |
| return o; | |
| } | |
| var geometryType = { | |
| LineString: line, | |
| MultiLineString: polygon, | |
| Polygon: polygon, | |
| MultiPolygon: function(arcs) { return arcs.map(polygon); } | |
| }; | |
| return o.type === "GeometryCollection" | |
| ? (o = Object.create(o), o.geometries = o.geometries.map(geometry), o) | |
| : geometry(o); | |
| } | |
| function reverse(array, n) { | |
| var t, j = array.length, i = j - n; while (i < --j) t = array[i], array[i++] = array[j], array[j] = t; | |
| } | |
| return { | |
| version: "0.0.2", | |
| mesh: mesh, | |
| object: object | |
| }; | |
| })(); |
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