var bb = {W:-5.0, N:50.0, E:10.0, S:40.0 }

svg.append("path")
.datum({type: "LineString", coordinates:
        [[-5, 40], [-5, 50], [10, 50], [10, 40], [-5, 40]]
       })
.attr("d", path);

bounds = [[-50.8,20.0][30,51.5]];
  WNES0 = bounds[0][0], // West    "W":-50.8
  WNES1 = bounds[1][1], // North   "N": 51.5
  WNES2 = bounds[1][0], // East    "E": 30
  WNES3 = bounds[0][1], // South   "S": 20.0

// *********** MATH TOOLKIT ********** //
function parallel(φ, λ0, λ1) {
  if (λ0 > λ1) λ1 += 360;
  var dλ = λ1 - λ0,
      step = dλ / Math.ceil(dλ);
  return d3.range(λ0, λ1 + .5 * step, step).map(function(λ) { return [normalise(λ), φ]; });
}
function normalise(x) {
  return (x + 180) % 360 - 180;
}

// *********** APPEND SHAPES ********** //
svg.append("path")
.datum({type: "Polygon", coordinates: [
    [[WNES0,WNES3]]
      .concat(parallel(WNES1, WNES0, WNES2))
      .concat(parallel(WNES3, WNES0, WNES2).reverse())
  ]})
.attr("d", path)
.style({'fill': '#B10000', 'fill-opacity': 0.3, 'stroke': '#B10000', 'stroke-linejoin': 'round'})
.style({'stroke-width': 1 });