A variation of my California population density map using California’s 23,198 block groups rather than its 8,043 tracts. The example exhibits how useful the Census API is: the prepublish script here can automatically grabs the list of counties for the desired state and then the population data for each block group.
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California Population Density II
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| license: gpl-3.0 | |
| height: 1100 | |
| border: no |
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| .DS_Store | |
| node_modules | |
| cb_* |
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| <!DOCTYPE html> | |
| <svg width="960" height="1100"></svg> | |
| <script src="https://d3js.org/d3.v4.min.js"></script> | |
| <script src="https://d3js.org/d3-scale-chromatic.v1.min.js"></script> | |
| <script src="https://d3js.org/topojson.v2.min.js"></script> | |
| <script> | |
| var svg = d3.select("svg"), | |
| width = +svg.attr("width"), | |
| height = +svg.attr("height"); | |
| var path = d3.geoPath(); | |
| var color = d3.scaleThreshold() | |
| .domain([1, 10, 50, 200, 500, 1000, 2000, 4000]) | |
| .range(d3.schemeOrRd[9]); | |
| var x = d3.scaleSqrt() | |
| .domain([0, 4500]) | |
| .rangeRound([440, 950]); | |
| var g = svg.append("g") | |
| .attr("class", "key") | |
| .attr("transform", "translate(0,40)"); | |
| g.selectAll("rect") | |
| .data(color.range().map(function(d) { | |
| d = color.invertExtent(d); | |
| if (d[0] == null) d[0] = x.domain()[0]; | |
| if (d[1] == null) d[1] = x.domain()[1]; | |
| return d; | |
| })) | |
| .enter().append("rect") | |
| .attr("height", 8) | |
| .attr("x", function(d) { return x(d[0]); }) | |
| .attr("width", function(d) { return x(d[1]) - x(d[0]); }) | |
| .attr("fill", function(d) { return color(d[0]); }); | |
| g.append("text") | |
| .attr("class", "caption") | |
| .attr("x", x.range()[0]) | |
| .attr("y", -6) | |
| .attr("fill", "#000") | |
| .attr("text-anchor", "start") | |
| .attr("font-weight", "bold") | |
| .text("Population per square mile"); | |
| g.call(d3.axisBottom(x) | |
| .tickSize(13) | |
| .tickValues(color.domain())) | |
| .select(".domain") | |
| .remove(); | |
| d3.json("topo.json", function(error, topology) { | |
| if (error) throw error; | |
| svg.append("g") | |
| .selectAll("path") | |
| .data(topojson.feature(topology, topology.objects.blockgroups).features) | |
| .enter().append("path") | |
| .attr("fill", function(d) { return d3.schemeOrRd[9][d.id]; }) | |
| .attr("d", path); | |
| svg.append("path") | |
| .datum(topojson.feature(topology, topology.objects.counties)) | |
| .attr("fill", "none") | |
| .attr("stroke", "#000") | |
| .attr("stroke-opacity", 0.3) | |
| .attr("d", path); | |
| }); | |
| </script> |
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| { | |
| "private": true, | |
| "license": "gpl-3.0", | |
| "author": { | |
| "name": "Mike Bostock", | |
| "url": "https://bost.ocks.org/mike" | |
| }, | |
| "scripts": { | |
| "prepublish": "bash prepublish" | |
| }, | |
| "devDependencies": { | |
| "d3-array": "^1.0.1", | |
| "d3-geo-projection": "^1.2.0", | |
| "ndjson-cli": "^0.3.0", | |
| "shapefile": "^0.5.8", | |
| "topojson": "^2.0.0", | |
| "topojson-client": "^2.1.0", | |
| "topojson-simplify": "^2.0.0" | |
| } | |
| } |
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| #!/bin/bash | |
| # EPSG:3310 California Albers | |
| PROJECTION='d3.geoAlbers().parallels([34, 40.5]).rotate([120, 0])' | |
| # The state FIPS code. | |
| STATE=06 | |
| # The ACS 5-Year Estimate vintage. | |
| YEAR=2014 | |
| # The display size. | |
| WIDTH=960 | |
| HEIGHT=1100 | |
| # Download the census block group boundaries. | |
| # Extract the shapefile (.shp) and dBASE (.dbf). | |
| if [ ! -f cb_${YEAR}_${STATE}_bg_500k.shp ]; then | |
| curl -o cb_${YEAR}_${STATE}_bg_500k.zip \ | |
| "http://www2.census.gov/geo/tiger/GENZ${YEAR}/shp/cb_${YEAR}_${STATE}_bg_500k.zip" | |
| unzip -o \ | |
| cb_${YEAR}_${STATE}_bg_500k.zip \ | |
| cb_${YEAR}_${STATE}_bg_500k.shp \ | |
| cb_${YEAR}_${STATE}_bg_500k.dbf | |
| fi | |
| # Download the list of counties. | |
| if [ ! -f cb_${YEAR}_${STATE}_counties.json ]; then | |
| curl -o cb_${YEAR}_${STATE}_counties.json \ | |
| "http://api.census.gov/data/${YEAR}/acs5?get=NAME&for=county:*&in=state:${STATE}&key=${CENSUS_KEY}" | |
| fi | |
| # Download the census block group population estimates for each county. | |
| if [ ! -f cb_${YEAR}_${STATE}_bg_B01003.ndjson ]; then | |
| for COUNTY in $(ndjson-cat cb_${YEAR}_${STATE}_counties.json \ | |
| | ndjson-split \ | |
| | tail -n +2 \ | |
| | ndjson-map 'd[2]' \ | |
| | cut -c 2-4); do | |
| echo ${COUNTY} | |
| if [ ! -f cb_${YEAR}_${STATE}_${COUNTY}_bg_B01003.json ]; then | |
| curl -o cb_${YEAR}_${STATE}_${COUNTY}_bg_B01003.json \ | |
| "http://api.census.gov/data/${YEAR}/acs5?get=B01003_001E&for=block+group:*&in=state:${STATE}+county:${COUNTY}&key=${CENSUS_KEY}" | |
| fi | |
| ndjson-cat cb_${YEAR}_${STATE}_${COUNTY}_bg_B01003.json \ | |
| | ndjson-split \ | |
| | tail -n +2 \ | |
| >> cb_${YEAR}_${STATE}_bg_B01003.ndjson | |
| done | |
| fi | |
| # 1. Convert to GeoJSON. | |
| # 2. Project. | |
| # 3. Join with the census data. | |
| # 4. Compute the population density. | |
| # 5. Simplify. | |
| # 6. Compute the county borders. | |
| geo2topo -n \ | |
| blockgroups=<(ndjson-join 'd.id' \ | |
| <(shp2json cb_${YEAR}_${STATE}_bg_500k.shp \ | |
| | geoproject "${PROJECTION}.fitExtent([[10, 10], [${WIDTH} - 10, ${HEIGHT} - 10]], d)" \ | |
| | ndjson-split 'd.features' \ | |
| | ndjson-map 'd.id = d.properties.GEOID.slice(2), d') \ | |
| <(ndjson-map < cb_${YEAR}_${STATE}_bg_B01003.ndjson '{id: d[2] + d[3] + d[4], B01003: +d[0]}') \ | |
| | ndjson-map -r d3=d3-array 'd[0].properties = {density: d3.bisect([1, 10, 50, 200, 500, 1000, 2000, 4000], (d[1].B01003 / d[0].properties.ALAND || 0) * 2589975.2356)}, d[0]') \ | |
| | topomerge -k 'd.id.slice(0, 3)' counties=blockgroups \ | |
| | topomerge --mesh -f 'a !== b' counties=counties \ | |
| | topomerge -k 'd.properties.density' blockgroups=blockgroups \ | |
| | toposimplify -p 1 -f \ | |
| > topo.json | |
| # Re-compute the topology as a further optimization. | |
| # This consolidates unique sequences of arcs. | |
| # https://github.com/topojson/topojson-simplify/issues/4 | |
| topo2geo \ | |
| < topo.json \ | |
| blockgroups=blockgroups.json \ | |
| counties=counties.json | |
| geo2topo \ | |
| blockgroups=blockgroups.json \ | |
| counties=counties.json \ | |
| | topoquantize 1e5 \ | |
| > topo.json | |
| rm blockgroups.json counties.json |
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