source/php/Helper/QueryEvents.php
public static function getNearbyLocations($lat, $lng, $distance = 0)
    {
        global $wpdb;

        // Radius of the earth in kilometers.
        $earth_radius = 6371;
        $sql = $wpdb->prepare(
            "
                SELECT DISTINCT
                    latitude.post_id,
                    post.post_title,
                    latitude.meta_value as lat,
                    longitude.meta_value as lng,
                    (%s * ACOS(
                        COS(RADIANS( %s )) * COS(RADIANS(latitude.meta_value)) * COS(
                        RADIANS(longitude.meta_value) - RADIANS( %s )
                        ) + SIN(RADIANS( %s )) * SIN(RADIANS(latitude.meta_value))
                    )) AS distance
                    FROM $wpdb->posts post
                    INNER JOIN $wpdb->postmeta latitude ON post.ID = latitude.post_id
                    INNER JOIN $wpdb->postmeta longitude ON post.ID = longitude.post_id
                    AND post.post_type   = 'event'
                    AND post.post_status = 'publish'
                    AND latitude.meta_key = 'latitude'
                    AND longitude.meta_key = 'longitude'
                    HAVING distance <= %s
                    ORDER BY distance ASC",
            $earth_radius,
            $lat,
            $lng,
            $lat,
            $distance
        );

        $nearby_locations = $wpdb->get_results($sql, ARRAY_A);

        if ($nearby_locations) {
            return $nearby_locations;
        }
    }
public static function getNearbyLocations($lat, $lng, $distance = 0)
    {
        global $wpdb;

        // Radius of the earth in kilometers.
        $earth_radius = 6371;
        $sql = $wpdb->prepare(
            "
                SELECT DISTINCT
                    latitude.post_id,
                    post.post_title,
                    latitude.meta_value as lat,
                    longitude.meta_value as lng,
                    (%s * ACOS(
                        COS(RADIANS( %s )) * COS(RADIANS(latitude.meta_value)) * COS(
                        RADIANS(longitude.meta_value) - RADIANS( %s )
                        ) + SIN(RADIANS( %s )) * SIN(RADIANS(latitude.meta_value))
                    )) AS distance
                    FROM $wpdb->posts post
                    INNER JOIN $wpdb->postmeta latitude ON post.ID = latitude.post_id
                    INNER JOIN $wpdb->postmeta longitude ON post.ID = longitude.post_id
                    AND post.post_type   = 'event'
                    AND post.post_status = 'publish'
                    AND latitude.meta_key = 'latitude'
                    AND longitude.meta_key = 'longitude'
                    HAVING distance <= %s
                    ORDER BY distance ASC",
            $earth_radius,
            $lat,
            $lng,
            $lat,
            $distance
        );

        $nearby_locations = $wpdb->get_results($sql, ARRAY_A);

        if ($nearby_locations) {
            return $nearby_locations;
        }
    }
Get event that occurs nearby a locations and within given distance
@param  string       $lat       latitude
@param  string       $lng       longitude
@param  int/float    $distance  radius distance in km
@return array with locations