Support directed bearing/orientation distributions and plots about osmnx HOT 5 CLOSED

Closed by #1139

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This would be easy enough to implement but I want to make sure that it's theoretically sound first. I think it may be, though users may need a warning to ensure things proceed according to expectations. That is, should we allow the calculation of bearings on directed graphs?

If a user is interested in the bearings/orientation of flows, then maybe yes. If the user is interested in the bearings/orientation of physical infrastructure, then no. Perhaps a UserWarning as such is sufficient if a user passes a MultiDiGraph instead of a MultiGraph.

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Thanks @gboeing for your insights here.

should we allow the calculation of bearings on directed graphs? If a user is interested in the bearings/orientation of flows, then maybe yes. If the user is interested in the bearings/orientation of physical infrastructure, then no.

That is a helpful conceptual distinction, although there is certainly a relation between physical infrastructure and flow. Some examples are waterways, separated highways, one ways trails (common in mountain biking, skiing, etc). In all these cases, the physical infrastructure is designed to support directional flow.

Perhaps a UserWarning as such is sufficient if a user passes a MultiDiGraph instead of a MultiGraph.

Another option would be to keep the "graph must be undirected" error unless the user sets an additional argument like directed_bearings=True or omit_reverse=True.

The warning proposal also sounds good paired with documentation like: "Supplying a MultiDiGraph results in directional bearings. For bidirectional bearings, use MultiDiGraph.to_undirected()".

One final note, I initially come to this repository with the hopes of using the bearing calculation and polar histogram plotting without wanting to use a networkx graph. But many of the critical functions required a graph input. Putting the data into the graph was not too hard, but for me was solely for purposes of using the mature and powerful bearing/plotting functionality.

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Would you like to open a PR (targeting the v2 branch) to allow directed graphs, issue a UserWarning and update the docstring?

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Would you like to open a PR (targeting the v2 branch) to allow directed graphs

Okay will do!

Nice to see the type annotations for v2... will make contributing easier.

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