This map dynamically simplifies the geometry in response to zooming, so that the smallest displayed detail is approximately one square pixel. Use the mousewheel, or pinch on touch devices, to zoom.
Dynamic Simplification IV
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
license: gpl-3.0 |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
<!DOCTYPE html> | |
<canvas width="960" height="500"></canvas> | |
<script src="https://d3js.org/d3.v4.min.js"></script> | |
<script src="https://unpkg.com/topojson-client@2"></script> | |
<script src="https://unpkg.com/topojson-simplify@2"></script> | |
<script> | |
var canvas = d3.select("canvas"), | |
context = canvas.node().getContext("2d"), | |
width = canvas.property("width"), | |
height = canvas.property("height"); | |
var land, | |
borders; | |
var minZ, // minimum area threshold for simplification | |
transform = d3.geoIdentity().clipExtent([[0, 0], [width, height]]), | |
simplify = d3.geoTransform({point: function(x, y, z) { if (z >= minZ) this.stream.point(x, y); }}); | |
var zoom = d3.zoom() | |
.scaleExtent([1 / (1 << 5), 1 << 2]) | |
.on("zoom", zoomed); | |
context.fillStyle = "#bbb"; | |
context.strokeStyle = "#fff"; | |
context.lineJoin = "round"; | |
context.lineCap = "round"; | |
var path = d3.geoPath() | |
.projection({stream: function(s) { return simplify.stream(transform.stream(s)); }}) | |
.context(context); | |
d3.json("us-states.json", function(error, us) { | |
if (error) throw error; | |
topojson.presimplify(us); | |
land = topojson.feature(us, us.objects.states); | |
borders = topojson.mesh(us, us.objects.states, function(a, b) { return a !== b; }); | |
// An arbitrary scale and center point to set the initial view. | |
// This projection is baked into the TopoJSON file, | |
// but is used here to compute the desired zoom translate. | |
var scale = 0.05, point = d3.geoMercator() | |
.translate([0, 0]) | |
.scale(4000) | |
([-75.959, 38.250]); | |
canvas | |
.call(zoom) | |
.call(zoom.transform, d3.zoomIdentity | |
.translate(width / 2, height / 2) | |
.scale(scale) | |
.translate(-point[0], -point[1])); | |
}); | |
function zoomed(d) { | |
var t = d3.event.transform; | |
minZ = 1 / (t.k * t.k); | |
transform.translate([t.x, t.y]).scale(t.k); | |
context.clearRect(0, 0, width, height); | |
context.beginPath(); | |
path(land); | |
context.fill(); | |
context.beginPath(); | |
path(borders); | |
context.stroke(); | |
} | |
</script> |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment