def _get_bounds_local(layers):
    """Aggregates bounding boxes of all local layers

        return: dict of bounding box of all bounds in layers
    """
    if not layers:
        return {'west': None, 'south': None, 'east': None, 'north': None}

    bounds = layers[0].bounds

    for layer in layers[1:]:
        bounds = np.concatenate(
            (
                np.minimum(
                    bounds[:2],
                    layer.bounds[:2]
                ),
                np.maximum(
                    bounds[2:],
                    layer.bounds[2:]
                )
            )
        )

    return dict(zip(['west', 'south', 'east', 'north'], bounds))
Aggregates bounding boxes of all local layers

        return: dict of bounding box of all bounds in layers