Defining a Projection

This is a simple example of defining a (not particularly useful) projection based on d3.geo.sinusoidal.

Every projection should also include an invert function.

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

.background {
  fill: #a4bac7;
}

.foreground {
  fill: none;
  stroke: #333;
  stroke-width: 1.5px;
}

.graticule {
  fill: none;
  stroke: #fff;
  stroke-width: .5px;
}

.graticule:nth-child(2n) {
  stroke-dasharray: 2,2;
}

</style>
<body>
<script src="https://cdn.jsdelivr.net/gh/mbostock/d3/projection/d3.v2.min.js"></script>
<script src="https://cdn.jsdelivr.net/gh/d3/d3-plugins/projection/geo/projection/projection.js"></script>
<script>
/* Define a new projection */
function cosinusoidal(λ, φ) {
    return [
      λ * Math.sin(φ),
      φ
    ];
  }

cosinusoidal.invert = function(x, y) {
  return [
    x / Math.sin(y),
    y
  ];
};

d3.geo.cosinusoidal = function() { return d3.geo.projection(cosinusoidal) };

/* Use the new projection */

var width = 960,
    height = 500;

var projection = d3.geo.cosinusoidal()
    .translate([width / 2 - .5, height / 2 - .5]);

var path = d3.geo.path()
    .projection(projection);

var graticule = d3.geo.graticule();

var svg = d3.select("body").append("svg")
    .attr("width", width)
    .attr("height", height);

svg.append("path")
    .datum(graticule.outline)
    .attr("class", "background")
    .attr("d", path);

svg.selectAll(".graticule")
    .data(graticule.lines)
  .enter().append("path")
    .attr("class", "graticule")
    .attr("d", path);

svg.append("path")
    .datum(graticule.outline)
    .attr("class", "foreground")
    .attr("d", path);

</script>

Updated missing url https://raw.github.com/mbostock/d3/projection/d3.v2.min.js to https://cdn.jsdelivr.net/gh/mbostock/d3/projection/d3.v2.min.js

Updated missing url https://raw.github.com/d3/d3-plugins/projection/geo/projection/projection.js to https://cdn.jsdelivr.net/gh/d3/d3-plugins/projection/geo/projection/projection.js

https://raw.github.com/mbostock/d3/projection/d3.v2.min.js

https://raw.github.com/d3/d3-plugins/projection/geo/projection/projection.js