Automatically define an Albers D3.js projection for a GeoJSON feature.

auto-map-projection.js

function framedProjection(feature, mapWidth, mapHeight) {
  var projection = d3.geoAlbers();

  var centroid = d3.geoCentroid(feature);

  projection.rotate([-1 * centroid[0]]).scale(1).translate([0, 0]);

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

  var bounds = path.bounds(feature);

  var scale = 0.618 / Math.max(
    (bounds[1][0] - bounds[0][0]) / mapWidth,
    (bounds[1][1] - bounds[0][1]) / mapHeight
  );

  var translate = [
    (mapWidth - scale * (bounds[1][0] + bounds[0][0])) / 2,
    (mapHeight - scale * (bounds[1][1] + bounds[0][1])) / 2
  ];

  projection.scale(scale).translate(translate);

  return projection;
}