def METHOD_NAME(self) -> SpatialMap[WidgetPlacement]:
    """A lazy-calculated spatial map."""
    if self._spatial_map is None:
        self._spatial_map = SpatialMap()
        self._spatial_map.insert(
            (
                placement.region.grow(placement.margin),
                placement.fixed,
                placement.overlay,
                placement,
            )
            for placement in self.placements
        )
    return self._spatial_map