if(!d3.geo2circle) d3.geo2circle = function(coordinates, radius) {
    radius = (radius) ? radius : Math.sqrt(Math.abs(area) / Math.PI)

	//circle 生成用の変数
	var circle = []
	var length = 0
	var lengths = [length]
	var p0 = coordinates[0]
	var p1
	var x
	var y
	var i = 0
	var n = coordinates.length

    
	// coordinatesの前後間の距離を求める
	while (++i < n) {
		p1 = coordinates[i]
		//console.log(p1);
		x = p1[0] - p0[0]
		y = p1[1] - p0[1]
		lengths.push(length += Math.sqrt(x * x + y * y))
		p0 = p1;
	}

    var centroid =d3.polygonCentroid(coordinates)
    var angle
    var i = -1
    var k = 2 * Math.PI / lengths[lengths.length - 1];

	// 円を描画するための座標を求める
	while (++i < n) {
		angle =  lengths[i] * k;
		circle.push([
			centroid[0] + radius * Math.cos(angle),
			centroid[1] + radius * Math.sin(angle)
		]);
	}

	return circle;
};