Spree now has a new zone feature. The feature allows you to define geographical areas for various purposes. Zones will initially be used to support highly customizable tax rate calculations. They are essentially a requirement to support sophisticated tax calculations where there are lots of exceptions. The VAT tax calculator in particular will require the use of such zones. Another possible use of zones will be for the upcoming shipping stuff. For more information on zones (and how to build them) you can see the wiki.