d3.geo.graticule = function() {

var x1, x0,

y1, y0,

dx = 22.5, dy = dx,

x, y,

precision = 2.5;

function graticule() {

return {type: "MultiLineString", coordinates: lines()};

}

function lines() {

return d3.range(Math.ceil(x0 / dx) * dx, x1, dx).map(x)

.concat(d3.range(Math.ceil(y0 / dy) * dy, y1, dy).map(y));

}

graticule.lines = function() {

return lines().map(function(coordinates) { return {type: "LineString", coordinates: coordinates}; });

}

graticule.outline = function() {

return {

type: "Polygon",

coordinates: [

x(x0).concat(

y(y1).slice(1),

x(x1).reverse().slice(1),

y(y0).reverse().slice(1))

]

};

};

graticule.extent = function(_) {

if (!arguments.length) return [[x0, y0], [x1, y1]];

x0 = +_[0][0], x1 = +_[1][0];

y0 = +_[0][1], y1 = +_[1][1];

if (x0 > x1) _ = x0, x0 = x1, x1 = _;

if (y0 > y1) _ = y0, y0 = y1, y1 = _;

return graticule.precision(precision);

};

graticule.step = function(_) {

if (!arguments.length) return [dx, dy];

dx = +_[0], dy = +_[1];

return graticule;

};

graticule.precision = function(_) {

if (!arguments.length) return precision;

precision = +_;

x = d3_geo_graticuleX(y0, y1, precision);

y = d3_geo_graticuleY(x0, x1, precision);

return graticule;

};

return graticule.extent([[-180 + ε, -90 + ε], [180 - ε, 90 - ε]]);

};

function d3_geo_graticuleX(y0, y1, dy) {

var y = d3.range(y0, y1 - ε, dy).concat(y1);

return function(x) { return y.map(function(y) { return [x, y]; }); };

}

function d3_geo_graticuleY(x0, x1, dx) {

var x = d3.range(x0, x1 - ε, dx).concat(x1);

return function(y) { return x.map(function(x) { return [x, y]; }); };

}