title: D3.geo : Spherical arcs rather than straight lines for parallels?
body: <p>I just made a D3js globe localisator, which looks like this :</p>
  
  <p><img src="https://i.stack.imgur.com/TuQm2.png" alt="enter image description here"></p>
  
  <p>If you look carefully, the red square looks ugly since it doesn't follow the Earth's curve. I have the area bounding box in decimal degrees :</p>
  
  <pre><code>var bb = {W:-5.0, N:50.0, E:10.0, S:40.0 }
  </code></pre>
  
  <p>And I draw the lines as follow:</p>
  
  <pre><code>svg.append("path")
  .datum({type: "LineString", coordinates: 
          [[-5, 40], [-5, 50], [10, 50], [10, 40], [-5, 40]]
         })
  .attr("d", path);
  </code></pre>
  
  <p>For larger areas, it's even the opposite curve from expectations (for a bounding box):</p>
  
  <p><img src="https://i.stack.imgur.com/SJNl5.png" alt="enter image description here"></p>
  
  <p><strong>How to add rather elegant spherical arcs ?</strong></p>