Question

I am trying to use D3 to render lines, but when I try to do this, the lines get rendered as polygons. I am not sure why. I included a screenshot to show you what it looks like.
Here is the code:

  // Creates a time scale using the x_extent
  // defined above
  var x_scale = d3.time.scale()
    .range([margin, width - margin])
    .domain(x_extent);

  // Creates a similarity scale using the y_extent.
  // defined above.
  var y_scale = d3.scale.linear()
    .range([height - margin, margin])
    .domain(y_extent);

  // Construct a line.
  var line = d3.svg.line()
    .x(function(d) {
      return x_scale(d.date);
    })
    .y(function(d) {
      return y_scale(d.similarity);
    });

  // Render a line.
  d3.select("svg")
    .append("path")
    .attr("d", line(data));

Answer 1

Try setting fill and stroke explicitly when appending the path, i.e.

d3.select("svg")
  .append("path")
  .attr("fill", "none")
  .attr("stroke", "black")
  .attr("d", line(data));