Basic Scatter Chart

This code example is the result of the Module 5's exercise from the course “Data Visualization and Infographics with D3,” taught by Alberto Cairo and Scott Murray, and offered through the Knight Center for Journalism in the Americas at UT Austin.
It is a simple scatter chart that plots two values of the underlying dataset (here: depth and magnitude of earthquakes) against each other.

<!DOCTYPE html>
<html lang="en">
	<head>
		<meta charset="utf-8">
		<link href='//fonts.googleapis.com/css?family=Open+Sans' rel='stylesheet' type='text/css'>
		<title>Exercise 5 - Scatterplot</title>
		<script type="text/javascript" src="https://d3js.org/d3.v3.js"></script>
		<style type="text/css">

body {
				font-family: 'Open Sans', sans-serif;
			}

.wrapper {
				position: relative;
				background-color: #843c39;
				width: 940px;
			}

header {
				background-color: #843c39;
				width: 940px;
				padding-bottom: 20px;
			}

h2 {
				font-family
				width: 940px;
				margin: 0 20px 5px 20px;
				padding-top: 10px;
				color: #fff4cb;
			}

span {
				font-size: 12px;
			}

p {
				margin: 5px 20px;
				color: #fff4cb;
				font-size: 14px;
				line-height: 1.1em;
			}

aside {
				position: absolute;
				width: 180px;
				bottom: 30px;
				left: 740px;
				background-color: #843c39;
			}

aside p {
				font-size: 12px;
			}

svg {
				fill: #843c39;
			}

rect {
				fill: #fff4cb;
			}

a {
				text-decoration: none;
				color: #bcbd22;
				font-weight: bold;
			}

circle.dot {
				fill: #bcbd22;
				stroke: #fff4cb;
				stroke-width: 1px;
			}

.axis path {
				stroke: #843c39;
				fill: none;
				shape-rendering: crispEdges;
			}

.axis line {
				fill: none;
				stroke: #fff4cb;
			}

.axis text {
				font-size: 12px;
				fill: #fff4cb;
			}

.label {
				stroke: #843c39;
			}
		</style>
	</head>
	<body>
		<div class="wrapper">
			<header>
				<h2>Seismic Events <span>&#8213; reported on March 20, 2015 between midnight and 8 a.m.</span></h2>
				<p>The scatter chart plots the relationship between depth and
					<a href="https://earthquake.usgs.gov/learn/glossary/?term=magnitude" target="_blank">
						magnitude
					</a>
					 of earthquakes.</p>
				<aside>
				<p>The data was taken from a
					<a href="https://earthquake.usgs.gov/earthquakes/feed/v1.0/csv.php" target="_blank">
						real-time feed
					</a>
					(including hourly, daily, weekly, and monthly feeds) provided by the website of
					<a href="https://earthquake.usgs.gov/" target="_blank">
						US Geological Survey (USGS).
					</a>
					It is a subset filtered by time to represent the events that occured between
					midnight and 8 a.m.
				</p>
			</aside>

</header>
		</div>
		<script type="text/javascript">
			var margin,
				width,
				height,
				xScale,
				yScale,
				xAxis,
				yAxis,
				svg,
				circles,
				xAxisGroup,
				yAxisGroup
				;

margin = {
				top: 20,
				right: 20,
				bottom: 30,
				left: 40
			};

width = 760 - margin.left - margin.right;
			height = 400 - margin.top - margin.bottom;

xScale = d3.scale.linear()
								.range([0, width - margin.right]);

yScale = d3.scale.linear()
								.range([height, 0]);

xAxis = d3.svg.axis()
								.scale(xScale)
								.orient("bottom")
								.ticks(10);

yAxis = d3.svg.axis()
								.scale(yScale)
								.orient("left");

svg = d3.select(".wrapper")
				.append("svg")
				.attr("width", width + margin.left + margin.right)
				.attr("height", height + margin.top + margin.bottom)
				.append("g")
				.attr("transform", "translate(" + margin.left + "," + margin.top + ")");

svg.append("rect")
				.attr("width", width)
				.attr("height", height);

// Filters the dataset by time to include only data points between
			// midnight and 8 a.m.
			function filterByTime(time) {
				var start,
					end,
					t;

// Start at midnight
				start = new Date(2015, 2, 20, 0, 0, 0).getTime();
				// End at 8 a.m.
				end = new Date(2015, 2, 20, 8, 0, 0).getTime();
				// Time the event occured
				t = new Date(time.time).getTime();

return start <= t && t <= end;
			}

d3.csv("earthquakes_all_day.csv", function(data) {
				var filteredByTime;

filteredByTime = data.filter(filterByTime);

filteredByTime.sort(function(a, b) {
					return d3.descending(a.mag, b.mag);
				});

xScale.domain(d3.extent(filteredByTime, function(d) {
					return +d.mag;
				})).nice();

yScale.domain(d3.extent(filteredByTime, function(d) {
					return +d.depth;
				})).nice();

circles = svg.selectAll("circle.dot")
					.data(filteredByTime, function(d, i) {
						return d.id;
					})
					.enter()
					.append("circle");

circles
					.attr("class", "dot")
					.attr("cx", function(d) {
						return xScale(d.mag);
					})
					.attr("cy", function(d, i) {
						return yScale(d.depth);
					})
					.attr("r", "0.1")
					.on("mouseover", function() {
						d3.select(this).attr("r", "12");
					})
					.on("mouseout", function() {
						d3.select(this).attr("r", "6");
					})
					.append("title")
					.text(function(d) {
						var dateTime;
						dateTime = new Date(d.time);
						return "At " + dateTime.toTimeString() + " on " + dateTime.toDateString() +
							" a " + d.type + " with a magnitude of " + d.mag +
							" and a depth of " + d.depth + " km occured in " + d.place;
					});

circles.sort(function(a, b) {
						return d3.ascending(a.depth, b.depth);
					})
					.transition()
					.delay(function(d, i) {
						return i * 50;
					})
					.duration(3000)
					.attr("r", "12")
					.transition()
					.duration(3000)
					.attr("r", "6");

xAxisGroup = svg.append("g")
					.attr("class", "x axis")
					.attr("transform", "translate(0, " + (height) + ")")
					.call(xAxis)
					.append("text")
					.attr("class", "label")
					.attr("x", width - 6)
					.attr("y", "-4")
					.style("text-anchor","end")
					.text("Magnitude");

yAxisGroup = svg.append("g")
					.attr("class", "y axis")
					.attr("transform", "translate(0,0)")
					.call(yAxis)
					.append("text")
					.attr("class", "label")
					.attr("transform", "rotate(-90)")
					.attr("x", "-4")
					.attr("dy", "1.1em")
					.style("text-anchor","end")
					.text("Depth (km)");
			});

</script>

</body>
</html>

Modified http://d3js.org/d3.v3.js to a secure url

https://d3js.org/d3.v3.js