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<canvas width="960" height="600"></canvas>
<p>
Blog post:
<a href="https://petrichor.studio/2018/05/21/get-started-creating-d3-maps/" target="_blank">
"Get Started Creating D3 Maps"
</a>
</p>
<p>
SVG version:
<a href="https://codepen.io/jwasilgeo/pen/NMedVV" target="_blank">
https://codepen.io/jwasilgeo/pen/NMedVV
</a>
</p>
<script src="https://d3js.org/d3.v5.min.js"></script>
<script src="https://unpkg.com/topojson-client@3.0.0/dist/topojson-client.min.js"></script>
body {
margin: 5px;
text-align: center;
background-color: #007da4;
}
canvas {
width: calc(100vmin - 10px);
outline: 1px solid white;
}
p, a {
color: white;
font-family: sans-serif;
font-size: 0.8rem;
}
// make D3 aware of the <canvas> element in the HTML
var canvas = d3.select("canvas");
var ctx = canvas.node().getContext("2d");
// get <canvas> width and height from HTML instead of hard-coding values
var canvasWidth = +canvas.attr("width"),
canvasHeight = +canvas.attr("height");
// define the map projection
// we're going from spherical latitude/longitude coordinates to a flat map
var projection = d3
// use Mercator for now, sigh, because of web map ubiquity...
.geoMercator()
// shift the projection translation offset to half of the parent <canvas> width and height
.translate([canvasWidth / 2, canvasHeight / 2])
// [0, 0] is redundant, but you could change the initial center [longitude, latitude]
.center([0, 0])
// [0, 0, 0] is also redundant, but you can change the rotation along 3 axes
// this property is really fun, so experiment with different values!
.rotate([0, 0, 0])
// set an initial scale value
.scale(canvasWidth / (2 * Math.PI));
// NOTE: if you want to skip setting the translate and scale values
// and instead zoom out to the whole world, you can just use this shortcut:
// projection.fitSize([canvasWidth, canvasHeight], {
// type: "Sphere"
// });
// "d3.geoPath" helps convert from geojson coordinates to <svg> or <canvas> drawing instructions
// it needs to know about the projection that was defined above
// and the <canvas> 2d rendering context
// I like to refer to it as a "geographic path generator" throughout the code
var geoPathGenerator = d3
.geoPath()
.projection(projection)
.context(ctx);
// request publicly available and hosted world topojson data,
// convert it to geojson,
// and then draw it in the <canvas>
d3
.json("https://unpkg.com/world-atlas@1.1.4/world/50m.json")
.then(function(loadedTopoJson) {
// use the concept of a topojson "mesh" to convert topojson
// to a single, efficient geojson geometry
var geoJson = topojson.mesh(
loadedTopoJson,
loadedTopoJson.objects.countries
);
// and then draw the single geojson representing all country polygons
// by giving explicit instructions to the <canvas> 2d rendering context
ctx.beginPath();
ctx.strokeStyle = "white";
ctx.lineWidth = 1;
ctx.lineJoin = "round";
ctx.lineCap = "round";
geoPathGenerator(geoJson);
ctx.stroke();
});
Also see: Tab Triggers