I’ve made a few bar charts up to this point. But really what I want to do is plot data over time. We need to figure out how to add x and y axis and work with x and y coordinates. The next logical step then, is to make a scatterplot.

A very Basic Scatterplot

A series of Steps

I’m beginning to lear that making anything is a series of steps in D3. It doesn’t really help you with the individual steps, but it does help you with lots of things to complete each step.

Some takeaways

The axis are really pretty easy. But what’s different is that you make a main <g> and then add axis to the main.

I didn’t really know how to style the axis. One big thing is that the axis look really fat until you apply a fill:none; either directly to the axis or in css.

I’m kind of struggling with the cx and cy. I understand how they are x and why coordinates, but I don’t understand how the data is coming from the object and being injected into the chart. I don’t really understand how you just ask for the scale and then the corresponding columns. That is a bit confusing. But other than that I think I get it.

Here’s a copy of this chart you can fork on observable: https://beta.observablehq.com/d/315e6f52aeab418a

<style>

.main text {
    font: 10px sans-serif;
}

.axis line, .axis path, path {
    shape-rendering: crispEdges;
    stroke: black;
    fill: none;
}


</style>
<svg class="scatterplot"></svg>
<script src="https://d3js.org/d3.v3.min.js"></script>
<script>
  var data = [
    [5, 3],
    [10, 17],
    [15, 4],
    [2, 8],
    [5,20],
    [15, 29],
    [12,42],
    [1,19],
    [6,4],
    [3,5],
    [30, 12],
    [34, 21],
    [8,26],
    [17, 20],
    [14,34],
    [1,16],
    [6,4],
    [21,5]
  ];
  var margin = { top: 20, right: 15, bottom: 60, left: 60  },
    width = 680 - margin.left - margin.right,
    height = 500 - margin.top - margin.bottom;

  var x = d3.scale.linear()
    .domain([0, d3.max(data, function(d) {
      return d[0];
    })])
    .range([0, width]);

  var y = d3.scale.linear()
    .domain([0, d3.max(data, function(d) {
      return d[1];
    })])
    .range([height, 0])

  var chart = d3.select('.scatterplot')
    .attr('width', width + margin.right + margin.left)
    .attr('height', height + margin.top + margin.bottom);

  var main = chart.append('g')
    .attr('transform', 'translate(' + margin.left + ',' + margin.right +')')
    .attr('width', width)
    .attr('height', height)
    .attr('class', 'main')

  //Draw the x and y axis.
  var xAxis = d3.svg.axis()
    .scale(x)
    .orient('bottom')

  main.append('g')
    .attr('transform', 'translate(0,' + height + ')')
    .attr('class', 'main axis date')
    .call(xAxis);

  var yAxis = d3.svg.axis()
    .scale(y)
    .orient('left')

  main.append('g')
    .attr('transform', 'translate(0,0)')
    .call(yAxis);

// Draw the X and Y Coordinates
  var g = main.append("svg:g")
    .attr("class", "added");

  g.selectAll("scatter-dots")
    .data(data)
      .enter().append("svg:circle")
        .attr("cx", function(d){ return x(d[0]);})
        .attr("cy", function(d){return y(d[1]);})
        .attr('r', 4)
        .attr('fill', 'none')
        .attr('stroke', 'steelblue')
        .attr('stroke-width',2)

</script>