| license: gpl-3.0 |
This demonstrates using topojson.merge, a new feature in TopoJSON 1.6, to merge multiple polygons into a single polygon whilst removing interior borders. (An alternative approach is to draw the polygons twice.)
This example is in response to a Stack Overflow question.
| <!DOCTYPE html> | |
| <meta charset="utf-8"> | |
| <style> | |
| .state { | |
| fill: #ccc; | |
| } | |
| .state-boundary { | |
| fill: none; | |
| stroke: #fff; | |
| } | |
| .state.selected { | |
| fill: orange; | |
| stroke: #000; | |
| } | |
| </style> | |
| <body> | |
| <script src="//d3js.org/d3.v3.min.js"></script> | |
| <script src="//d3js.org/topojson.v1.min.js"></script> | |
| <script> | |
| var width = 960, | |
| height = 600; | |
| var projection = d3.geo.albersUsa() | |
| .scale(1280) | |
| .translate([width / 2, height / 2]); | |
| var path = d3.geo.path() | |
| .projection(projection); | |
| var svg = d3.select("body").append("svg") | |
| .attr("width", width) | |
| .attr("height", height); | |
| var selected = d3.set([ | |
| 9, 10, 12, 13, 17, 18, 19, 21, 23, 24, | |
| 25, 26, 29, 31, 33, 34, 36, 37, 39, 42, | |
| 44, 45, 47, 50, 51, 54, 55 | |
| ]); | |
| d3.json("/mbostock/raw/4090846/us.json", function(error, us) { | |
| if (error) throw error; | |
| svg.append("path") | |
| .datum(topojson.feature(us, us.objects.states)) | |
| .attr("class", "state") | |
| .attr("d", path); | |
| svg.append("path") | |
| .datum(topojson.mesh(us, us.objects.states, function(a, b) { return a !== b; })) | |
| .attr("class", "state-boundary") | |
| .attr("d", path); | |
| svg.append("path") | |
| .datum(topojson.merge(us, us.objects.states.geometries.filter(function(d) { return selected.has(d.id); }))) | |
| .attr("class", "state selected") | |
| .attr("d", path); | |
| }); | |
| d3.select(self.frameElement).style("height", height + "px"); | |
| </script> |
How can I find the centroid of a merged shape?