# Find centerpoint of polygon in JavaScript

I have a “place” object from Google Maps which has a set of coordinates that represent a bounding box for a given location, say London. Each set of coordinates has a latitude and longitude.

I have written the below code to find the centerpoint, but I am not sure if it does actually produce the centerpoint. What if the polygon has 5 points instead of 4? Also, can this be done in a more efficient way, with less operations?

```function average(array) {
// Add together and then divide by the length
return _.reduce(array, function (sum, num) {
return sum + num;
}, 0) / array.length;
}

// I have a two-dimensional array that I want to get the average of

var coords = [
[ -1.2, 5.1 ],
[ -1.3, 5.2 ],
[ -1.8, 5.9 ],
[ -1.9, 5.8 ]
]

// So I get the first column

var lats = coords.map(function (coord) {
return coord[0];
})

// Then the second

var longs = coords.map(function (coord) {
return coord[1];
})

// And average each column out

console.log([average(lats), average(longs)])
```

This should get the centroid of the area of any polygon

```/*jslint sub: true, maxerr: 50, indent: 4, browser: true */
/*global console */

(function () {
"use strict";

function Point(x, y) {
this.x = x;
this.y = y;
}

function Region(points) {
this.points = points || [];
this.length = points.length;
}

Region.prototype.area = function () {
var area = 0,
i,
j,
point1,
point2;

for (i = 0, j = this.length - 1; i < this.length; j=i,i++) {
point1 = this.points[i];
point2 = this.points[j];
area += point1.x * point2.y;
area -= point1.y * point2.x;
}
area /= 2;

return area;
};

Region.prototype.centroid = function () {
var x = 0,
y = 0,
i,
j,
f,
point1,
point2;

for (i = 0, j = this.length - 1; i < this.length; j=i,i++) {
point1 = this.points[i];
point2 = this.points[j];
f = point1.x * point2.y - point2.x * point1.y;
x += (point1.x + point2.x) * f;
y += (point1.y + point2.y) * f;
}

f = this.area() * 6;

return new Point(x / f, y / f);
};

var polygon = [
{"x": -1.2, "y": 5.1},
{"x": -1.3, "y": 5.2},
{"x": -1.8, "y": 5.9},
{"x": -1.9, "y": 5.8}
],
region = new Region(polygon);

console.log(region.centroid());
}());
```

On jsfiddle

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