Public
Edited
Aug 1, 2023
22 forks
Importers
7 stars
Also listed in…
Gallery
County Maps
Insert cell
Insert cell
chart = {

// Join the geographic shapes and the population data.
const data = population.map((d) => ({
...d,
county: countymap.get(d.fips),
state: statemap.get(d.state)
}))
.filter(d => d.county)
.sort((a, b) => d3.descending(a.population, b.population));

// Construct the length scale.
const length = d3.scaleLinear([0, d3.max(data, d => d.population)], [0, 200]);

// Construct a path generator.
const path = d3.geoPath();

// Create the SVG container. Its dimensions correspond to the bounding-box
// of the pre-projected US shapefile.
const svg = d3.create("svg")
.attr("width", 975)
.attr("height", 610)
.attr("viewBox", [0, 0, 975, 610])
.attr("style", "width: 100%; height: auto; height: intrinsic;");

// Create the cartographic background layers.
svg.append("path")
.datum(topojson.feature(us, us.objects.nation))
.attr("fill", "#ddd")
.attr("d", path);

svg.append("path")
.datum(topojson.mesh(us, us.objects.states, (a, b) => a !== b))
.attr("fill", "none")
.attr("stroke", "white")
.attr("stroke-linejoin", "round")
.attr("d", path);

// Create the legend.
const legend = svg.append("g")
.attr("fill", "#777")
.attr("transform", "translate(886,592)")
.attr("text-anchor", "middle")
.style("font", "10px sans-serif")
.selectAll()
.data(length.ticks(4).slice(1))
.join("g")
.attr("transform", (d, i) => `translate(${20 * i},0)`);

legend.append("path")
.attr("fill", "red")
.attr("fill-opacity", 0.5)
.attr("stroke", "red")
.attr("stroke-width", 0.5)
.attr("d", d => spike(length(d)));

legend.append("text")
.attr("dy", "1em")
.text(length.tickFormat(4, "s"));

// Add a spike for each county, with a title (tooltip).
const format = d3.format(",.0f");
svg.append("g")
.attr("fill", "red")
.attr("fill-opacity", 0.5)
.attr("stroke", "red")
.attr("stroke-width", 0.5)
.selectAll()
.data(data)
.join("path")
.attr("transform", d => `translate(${centroid(d.county)})`)
.attr("d", d => spike(length(d.population)))
.append("title")
.text(d => `${d.county.properties.name}, ${d.state.properties.name}
${format(d.population)}`);

return svg.node();
}
Insert cell
Insert cell
population = FileAttachment("population.json").json()
.then((data) =>
data
.slice(1) // removes a header line
.map(([p, state, county]) => ({
state,
fips: `${state}${county}`,
population: +p
}))
)
Insert cell
Insert cell
centroid = {
const path = d3.geoPath();
return feature => path.centroid(feature);
}
Insert cell
Insert cell
us = FileAttachment("counties-albers-10m.json").json()
Insert cell
nation = topojson.feature(us, us.objects.nation)
Insert cell
statemap = new Map(topojson.feature(us, us.objects.states).features.map(d => [d.id, d]))
Insert cell
countymap = new Map(topojson.feature(us, us.objects.counties).features.map(d => [d.id, d]))
Insert cell
Insert cell
statemesh = topojson.mesh(us, us.objects.states, (a, b) => a !== b)
Insert cell
Insert cell
spike = (length, width = 7) => `M${-width / 2},0L0,${-length}L${width / 2},0`
Insert cell
Insert cell
Plot.plot({
width: 975,
projection: "identity",
length: {range: [0, 200]},
marks: [
Plot.geo(nation, { fill: "#eee" }),
Plot.geo(statemesh, { stroke: "white" }),
Plot.spike(population, Plot.centroid({length: "population", geometry: ({fips}) => countymap.get(fips)}))
]
})
Insert cell

One platform to build and deploy the best data apps

Experiment and prototype by building visualizations in live JavaScript notebooks. Collaborate with your team and decide which concepts to build out.
Use Observable Framework to build data apps locally. Use data loaders to build in any language or library, including Python, SQL, and R.
Seamlessly deploy to Observable. Test before you ship, use automatic deploy-on-commit, and ensure your projects are always up-to-date.
Learn more