How to add plotting scale？

[hengcall0]

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[pelson]

Please see the GitHub suggestions for the best way to get help with this kind of question https://github.com/SciTools/cartopy/blob/master/.github/SUPPORT.md. Something like StackOverflow would be a far better medium for such a question. There are also several such questions available on the internet - the top two google hits for "cartopy scale bar" are https://stackoverflow.com/questions/32333870/how-can-i-show-a-km-ruler-on-a-cartopy-matplotlib-plot and #490.

Finally, I think it is pretty likely that cartopy will gain such functionality built-in. I have a prototype in a branch, with and example of usage in https://github.com/pelson/cartopy/blob/scalebar/lib/cartopy/examples/scalebar.py. (this requires installing cartopy from source, using my branch to test).