Wording: "roi" vs "bounds" or "bounding box"

I know `roi` has been used in geff as well as spatial-graph.  But "roi" makes me think we're specifying a (possibly ephemeral) *subset* of the full sptial bounds of the graph.  Any thoughts about using `bounds` or `bounding_box` as well? 

(similar to the parent code:

```python
class SpatialGraph:
    ...
    @property
    def roi(self):
        return self._node_rtree.bounding_box()
```
