When downloading data, provide units for the 'positional_accuracy' field

It’s pretty obvious that it’s meters, I think. But it would be good practice to have that information readily available to all users.

Makes sense to me. Would vote if I had any left…

https://github.com/inaturalist/inaturalist/issues/2328

According to that issue, looks like this was decided not to be implemented, but pointed out that there need to be some general improvements to the metadata/export documentation. More on improvements to exports here: https://forum.inaturalist.org/t/data-users-what-are-your-use-cases-and-requests-for-exporting-data/2972