Allowed geometry types

[visr]

These types are properly in the docs and in Python as far as I can see. In the core we don't check them but we'll have to check them as part of #1729.

• Node: Point
• Edge: LineString or MultiLineString -> change to support only LineString
• Basin / area: Polygon or MultiPolygon -> change to support only MultiPolygon

One can wonder if we should support MultiLineString or not. We added it because one may want to model two routes (waterways) from A to B as one combined edge. And if you want your geometries to follow the waterways, you may then want to use a MultiLineString to show that this edge is either this or that connection. Though this is quite an esoteric situation that nobody really needs, so best to simplify this to LineString only.

Another thing we should check: We currently use GeoSeries[Any] from pandera. Can we tighten this to replace Any with the actual allowed geometry types?

In the QGIS plugin we currently pick one allowed geometry type per Basin. If we remove MultiLineString support, perhaps we should remove Polygon support for "Basin / area" so we always know all geometry types. It's easy to convert Polygon to MultiPolygon if needed. I think "Basin / area" needs to be MultiPolygon since one may want to model e.g. two tertiary canals that don't touch as one Basin.