score:6

Accepted answer

Your first point is at (137998238125800,-287) pixel coordinate, which is far away from the visible screen area. You don't use the selectAll/enter pattern which is at the core of D3. So you should start with this fundamental tutorial, then probably the code example you mention will make more sense:

var city = svg.selectAll(".city")
      .data(cities)
    .enter().append("g")
      .attr("class", "city");

  city.append("path")
      .attr("class", "line")
      .attr("d", function(d) { return line(d.values); })
      .style("stroke", function(d) { return color(d.name); });

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