Mapping Air Quality Data with D3 - VORONOI / Maya Gans

Maya Gans

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Sep 13, 2020

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import { hexdata } from '@enjalot/purpleair-historical-data'

hexdata

groupedData = d3.group(hexdata, d => d.day)

times = Array.from(groupedData.keys())

timeData = groupedData.get(currentTime)

points = timeData.map(d => [d.lng, d.lat, d.pm1])

md`### ${timeFormat(new Date(currentTime*1000))}`

mapSVG = svg`<svg width=${width} height=${height}>

<defs>

</clipPath>

</defs>

</svg>`

legend({color: colorPM1})

import {legend} from "@d3/color-legend"

projection = d3.geoAlbersUsa()

// magically fits map geography to width/height!

.fitSize([width, height], california[0])

path = d3.geoPath(projection)

colorPM1 = d3.scaleLinear()

.domain([0,50, 100, 150, 200, 250])

.range(["green", "yellow", "orange", "red", "maroon", "maroon"])

function render(svg) {

let svgSelection = d3.select(svg)

// california is an array with 1 element in it (the GeoJSON of its boundaries)

// the path function takes in a GeoJSON element and returns an SVG path string

// we can use this both to define the clippath and draw a boundary

let cali = path(california[0])

svgSelection.select("#californiaClip")

.select("path")

.attr('d', cali)

.attr('stroke', 'black')

.attr('fill', 'none');

// create the outline of california to clip our voronoi

// using https://observablehq.com/@manishearth/uc-california-voronoi-map

//what are defs

svgSelection.select("path.state")

// whats the dif between .data and .datum?

// When do you use each?

.attr("fill", "none")

.attr("stroke", "#111")

.attr("stroke-width", 6)

.attr("stroke-linejoin", "round")

.attr("d", cali);

svgSelection.select("g.voronoi")

// .append("g")

.attr("stroke", "none")

.attr("pointer-events", "all")

.selectAll("path")

.data(d3.geoVoronoi().polygons(points).features)

.join("path")

.attr("d", d3.geoPath(projection))

.attr("fill", d => colorPM1(d.properties.site[2]))

.attr("stroke", "black")

.attr("clip-path", "url(#californiaClip)");

return svgSelection;

}

timeFormat = d3.timeFormat("%Y-%m-%d %H:%M")

rendered = render(mapSVG)

height = 600

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