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Sep 23, 2024
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chart = Choropleth(unemployment, {
id: d => d.id,
value: d => d.rate,
scale: d3.scaleQuantize,
domain: [1, 10],
range: d3.schemeBlues[9],
title: (f, d) => `${f.properties.name}, ${statemap.get(f.id.slice(0, 2)).properties.name}\n${d?.rate}%`,
features: counties,
borders: statemesh,
width: 975,
height: 610
})
unemployment = (await FileAttachment("unemployment-x.csv").csv()).map(d => ({...d, rate: +d.rate}))
us = FileAttachment("counties-albers-10m.json").json()
counties = topojson.feature(us, us.objects.counties)
states = topojson.feature(us, us.objects.states)
statemap = new Map(states.features.map(d => [d.id, d]))
statemesh = topojson.mesh(us, us.objects.states, (a, b) => a !== b)
// Copyright 2021 Observable, Inc.
// Released under the ISC license.
// https://observablehq.com/@d3/choropleth
function Choropleth(data, {
id = d => d.id, // given d in data, returns the feature id
value = () => undefined, // given d in data, returns the quantitative value
title, // given a feature f and possibly a datum d, returns the hover text
format, // optional format specifier for the title
scale = d3.scaleSequential, // type of color scale
domain, // [min, max] values; input of color scale
range = d3.interpolateBlues, // output of color scale
width = 640, // outer width, in pixels
height, // outer height, in pixels
projection, // a D3 projection; null for pre-projected geometry
features, // a GeoJSON feature collection
featureId = d => d.id, // given a feature, returns its id
borders, // a GeoJSON object for stroking borders
outline = projection && projection.rotate ? {type: "Sphere"} : null, // a GeoJSON object for the background
unknown = "#ccc", // fill color for missing data
fill = "white", // fill color for outline
stroke = "white", // stroke color for borders
strokeLinecap = "round", // stroke line cap for borders
strokeLinejoin = "round", // stroke line join for borders
strokeWidth, // stroke width for borders
strokeOpacity, // stroke opacity for borders
} = {}) {
// Compute values.
const N = d3.map(data, id);
const V = d3.map(data, value).map(d => d == null ? NaN : +d);
const Im = new d3.InternMap(N.map((id, i) => [id, i]));
const If = d3.map(features.features, featureId);
// Compute default domains.
if (domain === undefined) domain = d3.extent(V);
// Construct scales.
const color = scale(domain, range);
if (color.unknown && unknown !== undefined) color.unknown(unknown);
// Compute titles.
if (title === undefined) {
format = color.tickFormat(100, format);
title = (f, i) => `${f.properties.name}\n${format(V[i])}`;
} else if (title !== null) {
const T = title;
const O = d3.map(data, d => d);
title = (f, i) => T(f, O[i]);
}
// Compute the default height. If an outline object is specified, scale the projection to fit
// the width, and then compute the corresponding height.
if (height === undefined) {
if (outline === undefined) {
height = 400;
} else {
const [[x0, y0], [x1, y1]] = d3.geoPath(projection.fitWidth(width, outline)).bounds(outline);
const dy = Math.ceil(y1 - y0), l = Math.min(Math.ceil(x1 - x0), dy);
projection.scale(projection.scale() * (l - 1) / l).precision(0.2);
height = dy;
}
}
// Construct a path generator.
const path = d3.geoPath(projection);
const svg = d3.create("svg")
.attr("width", width)
.attr("height", height)
.attr("viewBox", [0, 0, width, height])
.attr("style", "width: 100%; height: auto; height: intrinsic;");
if (outline != null) svg.append("path")
.attr("fill", fill)
.attr("stroke", "currentColor")
.attr("d", path(outline));
svg.append("g")
.selectAll("path")
.data(features.features)
.join("path")
.attr("fill", (d, i) => color(V[Im.get(If[i])]))
.attr("d", path)
.append("title")
.text((d, i) => title(d, Im.get(If[i])));
if (borders != null) svg.append("path")
.attr("pointer-events", "none")
.attr("fill", "none")
.attr("stroke", stroke)
.attr("stroke-linecap", strokeLinecap)
.attr("stroke-linejoin", strokeLinejoin)
.attr("stroke-width", strokeWidth)
.attr("stroke-opacity", strokeOpacity)
.attr("d", path(borders));
return Object.assign(svg.node(), {scales: {color}});
}
import {howto, linkplot} from "@d3/example-components"
import {Legend} from "@d3/color-legend"
Purpose-built for displays of data
Observable is your go-to platform for exploring data and creating expressive data visualizations. Use reactive JavaScript notebooks for prototyping and a collaborative canvas for visual data exploration and dashboard creation.
