Help! Can someone explain the algorithm for TimeZone::operator==? That is, how do you know if two time zones are the same or different?

I'm motivated by a UI design issue that's become hot around here. We allow users to select a time zone from a list. In our case, the list come from the ICU package, which I understand uses the same list as the Olsen package. Trouble is, this list is huge and bewildering, with a great deal of apparent redundancy. For example, there are 37 different time zones listed at GMT-04:00. This makes for a usability issue, as it becomes hard to search and confidently select the correct choice. And many are convinced that the long is just wrong because they can see a much shorter one used in Windows.

We want to generate a shorter list, but we're also reluctant to just throw out legitimate choices. If two time zones are equivalent, then it's OK to drop one from the list. But how can you tell? How does Windows do it?