Exploring Common Data Sets in v4: Iris Scatterplot (my take on a mbostock example)

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

body {
  font-size: 10px;
  font-family: Futura;
  background-color: black;
}

.axis {
  font-size: 8px;
  font-family: Futura;
  shape-rendering: crispEdges;
}

.axis text {

fill: white;

}

.legend text {

fill: white;

}

.dot {
  stroke: #000;
}

</style>
<body>
<script src="//d3js.org/d3.v4.min.js"></script>
<script>

var margin = {top: 20, right: 20, bottom: 30, left: 40},
    width = 660 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

var xScale = d3.scaleLinear()
    .range([0,width])

var yScale = d3.scaleLinear()
    .range([height, 0])

var x = d3.scaleLinear()
    .range([0, width]);

var y = d3.scaleLinear()
    .range([height, 0]);

var color = d3.scaleOrdinal(d3.schemeCategory20c);

var xAxis = d3.axisBottom(x)

var yAxis = d3.axisLeft(y)

var svg = d3.select("body").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 + ")");

d3.tsv("data.tsv", function(error, data) {
  if (error) throw error;

data.forEach(function(d) {
    d.sepalLength = +d.sepalLength;
    d.sepalWidth = +d.sepalWidth;
  });

x.domain(d3.extent(data, function(d) { return d.sepalWidth; })).nice();
  y.domain(d3.extent(data, function(d) { return d.sepalLength; })).nice();

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

svg.append("g")
      .attr("class", "y axis")
      .call(yAxis)
    .append("text")
      .attr("class", "label")
      .attr("transform", "rotate(-90)")
      .attr("y", 6)
      .attr("dy", ".71em")
      .style("text-anchor", "end")
      .text("Sepal Length (cm)")

svg.selectAll(".dot")
      .data(data)
    .enter().append("circle")
      .attr("class", "dot")
      .attr("r", 3.5)
      .attr("cx", function(d) { return x(d.sepalWidth); })
      .attr("cy", function(d) { return y(d.sepalLength); })
      .style("fill", function(d) { return color(d.species); });

var legend = svg.selectAll(".legend")
      .data(color.domain())
    .enter().append("g")
      .attr("class", "legend")
      .attr("transform", function(d, i) { return "translate(0," + i * 20 + ")"; });

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

legend.append("text")
      .attr("x", width - 24)
      .attr("y", 9)
      .attr("dy", ".35em")
      .style("text-anchor", "end")
      .text(function(d) { return d; });

});

</script>

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