Rough method for calculating a geographical midpoint, given a set of lat/lng pairs.

geo_midpoint.php

<?php
/**
 *  Rough method for calculating a geographical midpoint, given a set of lat/lng pairs.
 *  Assumes the earth is flat. This still gives a good approximation when deal with a small enough area.
 *  (eg. My use case is a handful of pubs in a particular part of town)
 */
function geo_midpoint($points) {

    $lats = array();
    $lngs = array();

    foreach($points as $p) {
        $lats[] = $p['lat'] + 90;
        $lngs[] = $p['lng'] + 180;
    }

    return array(
        'lat' => (array_sum($lats) / count($lats)) - 90;
        'lng' => (array_sum($lngs) / count($lngs)) - 180;
    );
}