@ajdawson - just wondering if you have more of these subclasses up your sleeve? If not, I'm inclined to suggest this becomes ```PlateCarreeFormatter``` - essentially I currently believe the ```GeoFormatter``` is an attempt to generalise a problem which only needs two solutions (Latitude & Longitude) and as a result has interfaces which make the implementation more complex than they (currently) need to be (e.g. `make_transform_args` and `extract_transform_result`). Is that an unfair observation? I'm happy to accept this complexity if there are potentially good cases for which this interface is useful, but I think it is worth knowing what they are even if we don't implement them just yet.