class-02 demo // source https://jsbin.com/tepewe

<!DOCTYPE html>
<meta charset="utf-8">
<title>class-02 demo</title>

// Set the map projection 
var projection = d3.geoAlbersUsa()
    .scale(7543)
    .translate([702, -186]);

var path = d3.geoPath()
    .pointRadius(5)
    .projection(projection);

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);

var layer1 = svg.append("g");
var layer2 = svg.append("g");

var base = "https://gist.githubusercontent.com/pbogden/935370a5272acff2618b/raw/f4d102d819066bb21a0021b4cbab6502e86bf587/";
var usgs = "https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_week.geojson";

// Read and plot the earthquake data
var url = base + "quakes.json";
d3.json(url, plotQuakes);
//d3.json(usgs, plotQuakes);

// Read and plot the state & county boundaries  
d3.json(base + "ok.json", plotState);

function plotQuakes(error, json) {
  if (error) console.log(error);
  
  // Assign the json to a global so we can manipulate it in the console
  data = json;
  
  // Filter the small earthquakes
  var features = data.features.filter(function(d) { return (+ d.properties.mag >= smallest) });

// Plot the earthquakes
  layer2.selectAll("path.quake")
      .data(features)
    .enter().append("path")
      .attr("class", "quake")
      .attr("d", path)
}

<body>
<script>
var width = 960, height = 500;
var data;  // declare a global variable
var layer = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height)
    .on("mousemove", mousemoved);
var info = d3.select("body").append("div")
    .attr("class", "info");
  
var projection = d3.geoAlbersUsa();
var path = d3.geoPath()
    .projection(projection);
  
// If you use this URL, you won't need your own copy of the data.
 
var url = "https://umbcvis.github.io/classes/class-03/us.json"
d3.json(url, plotStates);
function plotStates(error, json) {
  // Create array of GeoJSON features -- this defines the global variable "data"
  data = json.objects.us.geometries.map(function(d) { return topojson.feature(json, d); })

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

https://d3js.org/topojson.v2.min.js

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

https://d3js.org/topojson.v2.min.js