protected function computeMarkerShapes(Map $map)
    {
        $markerShapes = array();

        foreach ($map->getMarkers() as $marker) {
            if ($marker->hasShape() && !in_array($marker->getShape(), $markerShapes)) {
                $markerShapes[] = $marker->getShape();
            }
        }

        return $markerShapes;
    }