d3/_site/src/geo/mercator.js

A small, free JavaScript library for manipulating documents based on data.

d3.geo.mercator = function() {
  var scale = 500,
      translate = [480, 250];

  function mercator(coordinates) {
    var x = (coordinates[0]) / 360,
        y = (-180 / Math.PI * Math.log(Math.tan(Math.PI / 4 + coordinates[1] * Math.PI / 360))) / 360;
    return [
      scale * x + translate[0],
      scale * Math.max(-.5, Math.min(.5, y)) + translate[1]
    ];
  }

  mercator.scale = function(x) {
    if (!arguments.length) return scale;
    scale = +x;
    return mercator;
  };

  mercator.translate = function(x) {
    if (!arguments.length) return translate;
    translate = [+x[0], +x[1]];
    return mercator;
  };

  return mercator;
};