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Last active November 10, 2020 18:56
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Zoomable Geography
license: gpl-3.0

An example of d3.behavior.zoom and d3.geo.path. By modifying the transform, the browser can rapidly redraw geographic features while panning and zooming, without the overhead of reprojection. This technique can be extended by combining with d3.geo.tile.

#!/usr/bin/env node
var fs = require("fs");
var idProperty = process.argv[2],
collection = JSON.parse(fs.readFileSync("/dev/stdin")),
featureIds = {};
collection.features = collection.features.filter(function(feature) {
var id =[idProperty];
if (id == null) throw new Error("id is required for geouniq");
if (!(id in featureIds)) {
featureIds[id] = 1;
return true;
<!DOCTYPE html>
<meta charset="utf-8">
.overlay {
fill: none;
pointer-events: all;
.state {
fill: #aaa;
.state-border {
fill: none;
stroke: #fff;
stroke-linejoin: round;
stroke-linecap: round;
<script src="//"></script>
<script src="//"></script>
var width = 960,
height = 500;
var path = d3.geo.path()
var zoom = d3.behavior.zoom()
.translate([0, 0])
.scaleExtent([1, 8])
.on("zoom", zoomed);
var svg ="body").append("svg")
.attr("width", width)
.attr("height", height);
var features = svg.append("g");
.attr("class", "overlay")
.attr("width", width)
.attr("height", height)
d3.json("us.json", function(error, us) {
if (error) throw error;
.datum(topojson.feature(us, us.objects.states))
.attr("class", "state")
.attr("d", path);
.datum(topojson.mesh(us, us.objects.states, function(a, b) { return a !== b; }))
.attr("class", "state-border")
.attr("d", path)
.style("stroke-width", "1.5px");
.datum(topojson.mesh(us, us.objects.counties, function(a, b) { return a !== b && !( / 1000 ^ / 1000); }))
.attr("class", "county-border")
.attr("d", path)
.style("stroke-width", ".5px");
function zoomed() {
features.attr("transform", "translate(" + d3.event.translate + ")scale(" + d3.event.scale + ")");".state-border").style("stroke-width", 1.5 / d3.event.scale + "px");".county-border").style("stroke-width", .5 / d3.event.scale + "px");
}"height", height + "px");
"name": "anonymous",
"version": "0.0.1",
"private": true,
"devDependencies": {
"topojson": "1"
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I combined this example with raster tiles, also using as a blueprint. There is a small scaling problem when tile zoom levels change, but that could be caused by the rasterizer.

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