April 6 class

<!DOCTYPE html>
<meta charset="utf-8">
<style>

body {
  margin: 0;
}
.info {
  color: #000;
  position: absolute;
  top: 450px;
  left: 800px;
}
path {
  fill: none;
  stroke: red;
  stroke-linejoin: round;
  stroke-width: 1.5px;
}

</style>
<svg></svg>
<script src="//d3js.org/d3.v4.min.js"></script>
<script src="//d3js.org/d3-tile.v0.0.min.js"></script>
<script src="//d3js.org/topojson.v1.min.js"></script>
<script>

var pi = Math.PI,
    tau = 2 * pi;

var width = Math.max(960, window.innerWidth),
    height = Math.max(500, window.innerHeight);

// Initialize the projection to fit the world in a 1×1 square centered at the origin.
var projection = d3.geoMercator()
    .scale(1 / tau)
    .translate([0, 0]);
  
var info = d3.select("body").append("div")
    .attr("class", "info");
  
var path = d3.geoPath()
    .projection(projection);

var tile = d3.tile()
    .size([width, height]);

var zoom = d3.zoom()
    .scaleExtent([1 << 11, 1 << 14])
    .on("zoom", zoomed);

var svg = d3.select("svg")
    .attr("width", width)
    .attr("height", height)
.on("mousemove", mousemoved);

var raster = svg.append("g");
var vector = svg.append("path");
  var quakes = svg.append("g")

var us = "https://umbcvis.github.io/classes/class-03/us.json";
var usgs = "https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_week.geojson";

d3.queue()
    .defer(d3.json, us)
    .defer(d3.json, usgs)
    .await(ready);
  function ready(error, us, usgs) {
    if (error) throw error;

vector
      .datum(topojson.mesh(us, us.objects.us));
    
    
// Compute the projected initial center.
  var center = projection([-98.5, 39.5]);

quakes = quakes.selectAll(".quake")
.data(usgs.features)
.enter().append('path')
 .attr('class', 'quake')          
 .attr('d', path)
 .style('fill', 'crimson')

// Apply a zoom transform equivalent to projection.{scale,translate,center}.
  svg
      .call(zoom)
      .call(zoom.transform, d3.zoomIdentity
          .translate(width / 2, height / 2)
          .scale(1 << 12)
          .translate(-center[0], -center[1]));
}

function zoomed() {
  var transform = d3.event.transform;

var tiles = tile
      .scale(transform.k)
      .translate([transform.x, transform.y])
      ();

projection
      .scale(transform.k / tau)
      .translate([transform.x, transform.y]);

vector
      .attr("d", path);
  quakes.attr("d", path);

var image = raster
      .attr("transform", stringify(tiles.scale, tiles.translate))
    .selectAll("image")
    .data(tiles, function(d) { return d; });

image.exit().remove();

image.enter().append("image")
      .attr("xlink:href", function(d) { return "https://" + "abc"[d[1] % 3] + ".tile.openstreetmap.org/" + d[2] + "/" + d[0] + "/" + d[1] + ".png"; })
      .attr("x", function(d) { return d[0] * 256; })
      .attr("y", function(d) { return d[1] * 256; })
      .attr("width", 256)
      .attr("height", 256);
}

function stringify(scale, translate) {
  var k = scale / 256, r = scale % 1 ? Number : Math.round;
  return "translate(" + r(translate[0] * scale) + "," + r(translate[1] * scale) + ") scale(" + k + ")";
}
function mousemoved() {
  info.text(formatLocation(projection.invert(d3.mouse(this)), projection.scale()));
}

function formatLocation(p, k) {
  var format = d3.format("." + Math.floor(Math.log(k) / 2 - 2) + "f");
  return (p[1] < 0 ? format(-p[1]) + "°S" : format(p[1]) + "°N") + " "
       + (p[0] < 0 ? format(-p[0]) + "°W" : format(p[0]) + "°E");
}
</script>

https://d3js.org/d3.v4.min.js

https://d3js.org/d3-tile.v0.0.min.js

https://d3js.org/topojson.v1.min.js