This pull request fails (merged d636190 into cf7618c).

What do these magic numbers mean? Why is 20 of them better than 3 of them? (other than experimental evidence)
Perhaps these magic numbers could be dropped into the rcParams?

This change will need an entry in the api changelog.

Yes, so it's unclear. The FancyArrow docstring is also not clear about what they are. The kwarg width is the width of the arrow tail. Its default value is 0.001, but the docstring does not say what the units are. My first reaction was to say they in points, but I think thats too small. The kwarg head_width controls the width of the arrow head, its default is set to three times that of width. This would mean the units are the same but, again, I don't know what they are.

Would we prefer an rcParam for this instead? I'm starting to think that would be a better approach...

Would we prefer an rcParam for this instead?

I'm not sure about this now. The scale factor is only used when a user hasn't specified an arrow width - if the user were looking to change this they should set the width directly rather than setting a scale factor indirectly in rcParams.

Personally I'd be happy to merge this if you wouldn't mind re-basing?

Done.

👍. Anybody else want to comment? If not, I'll merge in the next 48 hrs.

Cheers @dmcdougall

@pelson Want to go ahead with this?