Alan D. Snow

Side note - I would recommend throwing some into the pyproj.CRS class and checking the ellipsoid attributes (semi_major_axis & semi_minor_axis).

@dopplershift, the error comes from the `setup.py` which is only used for the geodesic stuff. There really isn't any reason that the pin should be 8.0.0 in the setup,py. All...

> There really isn't any reason that the pin should be 8.0.0 in the setup,py Actually, I take that back. This setup has the potential to be unstable and isn't...

Once #1832 is resolved, this shouldn't be an issue (assuming you don't mind using the `pyproj` wheels).

> I was wondering whether it would be possible to make cartopy a little more backward compatible and extend support for proj < 8 in order to make life easier...

If the pin for `pyproj` is moved to 3.1+ [Transformer.transform_bounds](https://pyproj4.github.io/pyproj/stable/api/transformer.html#pyproj.transformer.Transformer.transform_bounds) could potentially be useful.

> maybe in a future PR? There may be other places in the code that would likely benefit from that as well, so a separate PR would be a better...

Here are performance tips identified in the pyproj development: 1. Using the global context for creating several PROJ objects [ref](https://pyproj4.github.io/pyproj/stable/advanced_examples.html#optimizing-single-threaded-applications) can improve performance. However, it is not thread safe. So,...

@maximlt, the updated method of PROJ is more robust when comparing CRS and has many different methods to create a CRS (PROJ string, Authority, WKT, PROJ JSON, etc...). Since `proj`...