ENH: Add support for PROJ_DATA environment variable

[snowman2]

Closes #1127

[sgillies]

@snowman2 I wonder how long we'll be supporting PROJ_LIB? A year or more? I think this will definitely hold for that long. Thank you!

[snowman2]

I wonder how long we'll be supporting PROJ_LIB? A year or more?

It will be dropped in PROJ 10 OSGeo/PROJ#3255, though I am not sure on the planned release date.

[jorisvandenbossche]

I wonder how long we'll be supporting PROJ_LIB?

You should probably keep it as long as you support PROJ versions that use that env variable? (which I suppose will be longer than a year)

[sgillies]

We have a numpy and GDAL version policy based on https://numpy.org/neps/nep-0029-deprecation_policy.html. We'll add PROJ. Even though fiona doesn't use the PROJ API (only via GDAL), there's no way around PROJ_LIB/PROJ_DATA.

[snowman2]

Thanks @sgillies 👍