regional variables

[edwindj]

Many tables of SN contain regional data: it would be nice if these tables can be converted into sf objects.

However:

• many maps of SN are time-dependent so the user should be expliciet in what year should be used to convert to sf
• would be nice to be not dependent on sf (only when installed).

[FrieseWoudloper]

This would be a nice feature for sure! I'd like to upvote it.