block by mbostock 20789c8df83e04e49684

Merging States

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Using topojson.merge to merge states & provinces into a single feature from the Natural Earth 1:10,000,000 Admin 1 dataset.

The orange arc is an artifact of the merge that might either be a bug in the merge algorithm or in the dataset (or both).

index.html

<!DOCTYPE html>
<meta charset="utf-8">
<style>

.graticule {
  fill: none;
  stroke: #777;
  stroke-opacity: .5;
  stroke-width: .5px;
  pointer-events: none;
}

.land {
  fill: #222;
  stroke: orange;
}

.border {
  fill: none;
  stroke: #fff;
  stroke-width: .5px;
}

</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 = 960;

var projection = d3.geo.mercator()
    .scale(width / 2 / Math.PI)
    .translate([width / 2, height / 2])
    .precision(.1);

var path = d3.geo.path()
    .projection(projection);

var graticule = d3.geo.graticule();

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);

svg.append("path")
    .datum(graticule)
    .attr("class", "graticule")
    .attr("d", path);

d3.json("world.json", function(error, world) {
  if (error) throw error;

  svg.insert("path", ".graticule")
      .datum(topojson.merge(world, world.objects.states.geometries))
      .attr("class", "land")
      .attr("d", path);

  svg.insert("path", ".graticule")
      .datum(topojson.mesh(world, world.objects.states, function(a, b) { return a !== b; }))
      .attr("class", "border")
      .attr("d", path);
});

d3.select(self.frameElement).style("height", height + "px");

</script>

Makefile

GENERATED_FILES = \
	world.json

all: $(GENERATED_FILES)

clean:
	rm -rf -- $(GENERATED_FILES)

.PHONY: all clean

build/ne_10m_%.zip:
	mkdir -p $(dir $@)
	curl -o $@ "http://www.nacis.org/naturalearth/10m/cultural/ne_10m_$*.zip"

build/ne_%_admin_1_states_provinces.shp: build/ne_%_admin_1_states_provinces_shp.zip
	mkdir -p $(dir $@)
	unzip -od $(dir $@) $<
	for file in $(dir $@)/ne_$*_admin_1_states_provinces_shp.*; do mv $$file $(dir $@)/ne_$*_admin_1_states_provinces"$${file#*_shp}"; done
	touch $@

world.json: build/ne_10m_admin_1_states_provinces.shp
	node_modules/.bin/topojson \
		-o $@ \
		-q 1e5 \
		--simplify-proportion .1 \
		-- states=$<

package.json

{
  "name": "anonymous",
  "version": "0.0.1",
  "private": true,
  "dependencies": {
    "topojson": "1"
  }
}