Equidistant map perimeter circles

README.md

Equidistant map perimeter circles circles

Made with blockup.

boundary.topojson

dist.css

.buttons{margin:0 auto;text-align:center}.map svg{display:block;margin:0 auto}.map svg circle{fill:#8f092a;fill-opacity:.25;stroke:#8f092a}

dist.js

var margin={top:10,right:10,bottom:10,left:10};d3.json("./boundary.topojson",function(t){var e=topojson.feature(t,t.objects.boundary),n=(d3.geoBounds(e),d3.geoCentroid(e),d3.geoAlbers()),r=d3.geoPath().projection(n),a=r.bounds(e),o=(a[1][0]-a[0][0])/(a[1][1]-a[0][1]),i=460,c=i*o,u=c-margin.left-margin.right,l=i-margin.top-margin.bottom,d=d3.select(".map svg").attrs({width:c,height:i}).append("g").attr("transform","translate("+margin.left+", "+margin.top+")");n.fitSize([u,l],e);var s=_(e.features).map("geometry").flatten().map("coordinates").flatten().sortBy("length").map(function(t){return turf.lineString(t)}).value(),f=_(s).map(function(t){return turf.lineDistance(t)}).sum(),m=1e3,g=m,p=_(s).map(function(t){var e=turf.lineDistance(t),n=Math.ceil(e*m/f),r=Math.min(g,n);g-=r;var a=e/r,o=d3.range(r).map(function(e){return turf.along(t,e*a)});return o}).flatten().map(function(t){return n(t.geometry.coordinates)}).value(),v=function(){var t=d.selectAll("circle").data(p);t.enter().append("circle").attrs({cx:u/2,cy:l/2,r:0}).transition("enter").duration(1e3).delay(function(t,e){return 10*e}).attrs({cx:function(t){return t[0]},cy:function(t){return t[1]},r:1})},y=function(){var t=d.selectAll("circle").data(p);t.transition("exit").duration(250).delay(function(t,e){return 2*e}).attrs({cx:u/2,cy:l/2,r:0}).remove()};v(),document.querySelector("button.enter").addEventListener("click",v),document.querySelector("button.exit").addEventListener("click",y)});
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b[0][0]) / (b[1][1] - b[0][1])\n\n\tconst outerHeight = 460\n\tconst outerWidth = outerHeight * aspect\n\n\tconst width = outerWidth - margin.left - margin.right\n\tconst height = outerHeight - margin.top - margin.bottom\n\n\t// Prepare svg.\n\tconst g = d3.select('.map svg')\n\t\t\t.attrs({ width: outerWidth, height: outerHeight })\n\t\t.append('g')\n\t\t\t.attr('transform', `translate(${margin.left}, ${margin.top})`)\n\n\t// Fit the feature to the container's width.\n\tprojection.fitSize([width, height], feature)\n\n\t// Get the individual line strings.\n\tconst lineStrings = _(feature.features)\n\t\t.map('geometry')\n\t\t.flatten()\n\t\t.map('coordinates')\n\t\t.flatten()\n\t\t.sortBy('length')\n\t\t.map(d => turf.lineString(d))\n\t\t.value()\n\n\t// Calculate the overall line string length.\n\tconst totalLength = _(lineStrings)\n\t\t.map(d => turf.lineDistance(d))\n\t\t.sum()\n\n\t// Desired number of total points.\n\tconst pointsCount = 1000\n\tlet pointsRemaining = pointsCount\n\n\tconst points = _(lineStrings)\n\t\t.map(line => {\n\n\t\t\t// How many points will this line get?\n\n\t\t\t// First, calculate this line's length.\n\t\t\tconst lineLength = turf.lineDistance(line)\n\n\t\t\t// Next, get this line's points proportion, rounded up.\n\t\t\tconst upperCount = Math.ceil(lineLength * pointsCount / totalLength)\n\n\t\t\t// Don't get more points that are available.\n\t\t\tconst linePointsCount = Math.min(pointsRemaining, upperCount)\n\n\t\t\t// Make sure to update points remaining.\n\t\t\tpointsRemaining -= linePointsCount\n\n\t\t\t// Now that we know how many points this line will get,\n\t\t\t// calculate the distance between points - the step:\n\t\t\tconst step = lineLength / linePointsCount\n\n\t\t\tconst linePoints = d3.range(linePointsCount)\n\t\t\t\t.map(d => turf.along(line, d * step))\n\n\t\t\treturn linePoints\n\n\t\t})\n\t\t.flatten()\n\t\t.map(d => projection(d.geometry.coordinates))\n\t\t.value()\n\n\t// This function adds the circles.\n\tconst enter = () => {\n\n\t\t// JOIN new data with old elements.\n\t\tconst circles = g.selectAll('circle')\n\t\t\t\t.data(points)\n\n\t\t// ENTER new elements present in new data.\n\t\tcircles.enter().append('circle')\n\t\t\t\t.attrs({\n\t\t\t\t\tcx: width/2,\n\t\t\t\t\tcy: height/2,\n\t\t\t\t\tr: 0,\n\t\t\t\t})\n\t\t\t.transition('enter')\n\t\t\t\t.duration(1000)\n\t\t\t\t.delay((d, i) => i * 10)\n\t\t\t\t.attrs({\n\t\t\t\t\tcx: d => d[0],\n\t\t\t\t\tcy: d => d[1],\n\t\t\t\t\tr: 1,\n\t\t\t\t})\n\n\t}\n\n\t// This function removes the circles.\n\tconst exit = () => {\n\n\t\t// JOIN new data with old elements.\n\t\tconst circles = g.selectAll('circle')\n\t\t\t\t.data(points)\n\n\t\t// UPDATE old elements present in new data.\n\t\tcircles\n\t\t\t.transition('exit')\n\t\t\t\t.duration(250)\n\t\t\t\t.delay((d, i) => i * 2)\n\t\t\t\t.attrs({\n\t\t\t\t\tcx: width/2,\n\t\t\t\t\tcy: height/2,\n\t\t\t\t\tr: 0,\n\t\t\t\t})\n\t\t\t.remove()\n\n\t}\n\n\t// Fire the enter function on page load.\n\tenter()\n\n\t// Listen to button clicks.\n\tdocument.querySelector('button.enter').addEventListener('click', enter)\n\tdocument.querySelector('button.exit').addEventListener('click', exit)\n\n})\n"]}

index.html

<!DOCTYPE html>
<title>Equidistant outline circles</title>
<link href='dist.css' rel='stylesheet' />
<body>
	<div class='map'>
		<svg></svg>
	</div>
	<div class='buttons'>
		<button class='enter'>Enter</button>
		<button class='exit'>Exit</button>
	</div>
	<script src='https://d3js.org/d3.v4.min.js'></script>
	<script src='https://d3js.org/d3-selection-multi.v1.min.js'></script>
	<script src='https://d3js.org/topojson.v2.min.js'></script>
	<script src='https://npmcdn.com/@turf/[email protected]/turf.min.js'></script>
	<script src='https://cdn.jsdelivr.net/lodash/4.17.4/lodash.min.js'></script>
	<script src='dist.js'></script>
</body>

Makefile

all:

	rm boundary.topojson;
	mapshaper -i ~/Downloads/cb_2015_us_nation_5m/cb_2015_us_nation_5m.shp name=boundary -clip bbox=-126,23,-65,50 -filter-slivers min-area=700000000 -lines -simplify dp 5% -o format=topojson boundary.topojson;

preview.png

script.js

// Setup chart dimensions.
const margin = { top: 10, right: 10, bottom: 10, left: 10 }

// Get GeoJSON.
d3.json('./boundary.topojson', json => {

	const feature = topojson.feature(json, json.objects.boundary)

	// Get feature's bounds and centroid.
	const bounds = d3.geoBounds(feature)
	const centroid = d3.geoCentroid(feature)

	// const projection = d3.geoConicConformal()
	// 	.parallels([bounds[0][1], bounds[1][1]])
	// 	.rotate([-centroid[0], 0])
	// 	.center([0, -centroid[1]])

	const projection = d3.geoAlbers()

	// Get the path.
	const path = d3.geoPath().projection(projection)

	// Get the path's bounds (i.e., in pixels).
	const b = path.bounds(feature)

	// Get aspect ratio.
	const aspect = (b[1][0] - b[0][0]) / (b[1][1] - b[0][1])

	const outerHeight = 460
	const outerWidth = outerHeight * aspect

	const width = outerWidth - margin.left - margin.right
	const height = outerHeight - margin.top - margin.bottom

	// Prepare svg.
	const g = d3.select('.map svg')
			.attrs({ width: outerWidth, height: outerHeight })
		.append('g')
			.attr('transform', `translate(${margin.left}, ${margin.top})`)

	// Fit the feature to the container's width.
	projection.fitSize([width, height], feature)

	// Get the individual line strings.
	const lineStrings = _(feature.features)
		.map('geometry')
		.flatten()
		.map('coordinates')
		.flatten()
		.sortBy('length')
		.map(d => turf.lineString(d))
		.value()

	// Calculate the overall line string length.
	const totalLength = _(lineStrings)
		.map(d => turf.lineDistance(d))
		.sum()

	// Desired number of total points.
	const pointsCount = 1000
	let pointsRemaining = pointsCount

	const points = _(lineStrings)
		.map(line => {

			// How many points will this line get?

			// First, calculate this line's length.
			const lineLength = turf.lineDistance(line)

			// Next, get this line's points proportion, rounded up.
			const upperCount = Math.ceil(lineLength * pointsCount / totalLength)

			// Don't get more points that are available.
			const linePointsCount = Math.min(pointsRemaining, upperCount)

			// Make sure to update points remaining.
			pointsRemaining -= linePointsCount

			// Now that we know how many points this line will get,
			// calculate the distance between points - the step:
			const step = lineLength / linePointsCount

			const linePoints = d3.range(linePointsCount)
				.map(d => turf.along(line, d * step))

			return linePoints

		})
		.flatten()
		.map(d => projection(d.geometry.coordinates))
		.value()

	// This function adds the circles.
	const enter = () => {

		// JOIN new data with old elements.
		const circles = g.selectAll('circle')
				.data(points)

		// ENTER new elements present in new data.
		circles.enter().append('circle')
				.attrs({
					cx: width/2,
					cy: height/2,
					r: 0,
				})
			.transition('enter')
				.duration(1000)
				.delay((d, i) => i * 10)
				.attrs({
					cx: d => d[0],
					cy: d => d[1],
					r: 1,
				})

	}

	// This function removes the circles.
	const exit = () => {

		// JOIN new data with old elements.
		const circles = g.selectAll('circle')
				.data(points)

		// UPDATE old elements present in new data.
		circles
			.transition('exit')
				.duration(250)
				.delay((d, i) => i * 2)
				.attrs({
					cx: width/2,
					cy: height/2,
					r: 0,
				})
			.remove()

	}

	// Fire the enter function on page load.
	enter()

	// Listen to button clicks.
	document.querySelector('button.enter').addEventListener('click', enter)
	document.querySelector('button.exit').addEventListener('click', exit)

})

style.styl

$red = #8f092a

.buttons
	margin 0 auto
	text-align center

.map

	svg
		display block
		margin 0 auto

		circle
			fill $red
			fill-opacity 0.25
			stroke $red

thumbnail.png