Basic US State Map - D3

My first D3 map showing my travel across the US. This visualization was built by modifying choropleth example code by Scott Murray, tooltip example code by Malcolm Maclean, and legend code example by Mike Bostock.

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<script src="https://d3js.org/d3.v3.min.js"></script>
<style type="text/css">

/* On mouse hover, lighten state color */
path:hover {
	fill-opacity: .7;
}

/* Style for Custom Tooltip */
div.tooltip {   
 	position: absolute;           
	text-align: center;           
	width: 60px;                  
	height: 28px;                 
	padding: 2px;             
	font: 12px sans-serif;        
	background: white;   
	border: 0px;      
	border-radius: 8px;           
	pointer-events: none;         
}
        
/* Legend Font Style */
body {
	font: 11px sans-serif;
}
        
/* Legend Position Style */
.legend {
	position:absolute;
	left:800px;
	top:350px;
}

</style>
</head>
<body>
<script type="text/javascript">

/*  This visualization was made possible by modifying code provided by:

Scott Murray, Choropleth example from "Interactive Data Visualization for the Web" 
  */

//Width and height of map
var width = 960;
var height = 500;

// D3 Projection
var projection = d3.geo.albersUsa()
				   .translate([width/2, height/2])    // translate to center of screen
				   .scale([1000]);          // scale things down so see entire US
        
// Define path generator
var path = d3.geo.path()               // path generator that will convert GeoJSON to SVG paths
		  	 .projection(projection);  // tell path generator to use albersUsa projection

// Define linear scale for output
var color = d3.scale.linear()
			  .range(["rgb(213,222,217)","rgb(69,173,168)","rgb(84,36,55)","rgb(217,91,67)"]);

var legendText = ["Cities Lived", "States Lived", "States Visited", "Nada"];

//Create SVG element and append map to the SVG
var svg = d3.select("body")
			.append("svg")
			.attr("width", width)
			.attr("height", height);
        
// Append Div for tooltip to SVG
var div = d3.select("body")
		    .append("div")   
    		.attr("class", "tooltip")               
    		.style("opacity", 0);

// Load in my states data!
d3.csv("stateslived.csv", function(data) {
color.domain([0,1,2,3]); // setting the range of the input data

// Load GeoJSON data and merge with states data
d3.json("us-states.json", function(json) {

// Loop through each state data value in the .csv file
for (var i = 0; i < data.length; i++) {

// Grab State Name
	var dataState = data[i].state;

// Grab data value 
	var dataValue = data[i].visited;

// Find the corresponding state inside the GeoJSON
	for (var j = 0; j < json.features.length; j++)  {
		var jsonState = json.features[j].properties.name;

if (dataState == jsonState) {

// Copy the data value into the JSON
		json.features[j].properties.visited = dataValue;

// Stop looking through the JSON
		break;
		}
	}
}
		
// Bind the data to the SVG and create one path per GeoJSON feature
svg.selectAll("path")
	.data(json.features)
	.enter()
	.append("path")
	.attr("d", path)
	.style("stroke", "#fff")
	.style("stroke-width", "1")
	.style("fill", function(d) {

// Get data value
	var value = d.properties.visited;

if (value) {
	//If value exists…
	return color(value);
	} else {
	//If value is undefined…
	return "rgb(213,222,217)";
	}
});

// Map the cities I have lived in!
d3.csv("cities-lived.csv", function(data) {

svg.selectAll("circle")
	.data(data)
	.enter()
	.append("circle")
	.attr("cx", function(d) {
		return projection([d.lon, d.lat])[0];
	})
	.attr("cy", function(d) {
		return projection([d.lon, d.lat])[1];
	})
	.attr("r", function(d) {
		return Math.sqrt(d.years) * 4;
	})
		.style("fill", "rgb(217,91,67)")	
		.style("opacity", 0.85)

// Modification of custom tooltip code provided by Malcolm Maclean, "D3 Tips and Tricks" 
	
	.on("mouseover", function(d) {      
    	div.transition()        
      	   .duration(200)      
           .style("opacity", .9);      
           div.text(d.place)
           .style("left", (d3.event.pageX) + "px")     
           .style("top", (d3.event.pageY - 28) + "px");    
	})

// fade out tooltip on mouse out               
    .on("mouseout", function(d) {       
        div.transition()        
           .duration(500)      
           .style("opacity", 0);   
    });
});  
        
// Modified Legend Code from Mike Bostoc
var legend = d3.select("body").append("svg")
      			.attr("class", "legend")
     			.attr("width", 140)
    			.attr("height", 200)
   				.selectAll("g")
   				.data(color.domain().slice().reverse())
   				.enter()
   				.append("g")
     			.attr("transform", function(d, i) { return "translate(0," + i * 20 + ")"; });

legend.append("rect")
   		  .attr("width", 18)
   		  .attr("height", 18)
   		  .style("fill", color);

legend.append("text")
  		  .data(legendText)
      	  .attr("x", 24)
      	  .attr("y", 9)
      	  .attr("dy", ".35em")
      	  .text(function(d) { return d; });
	});

});
</script>
</body>
</html>

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