Package tz provides a wrapper for time.Location with additional information about timezones.

Every timezone is represented by a zone name (Europe/Amsterdam) and a country (NL). The rationale for this is mostly a user interface one: it makes more sense to display a list of countries first and then a list of timezones, instead of just presenting a huge list of timezones.

For example, my current TZ is Asia/Makkasar (WITA), but it's much easier to select "Indonesia" from a list, and then choose one of the four timezones in Indonesia:

Indonesia: Asia/Jayapura (WIT) – New Guinea (West Papua / Irian Jaya); Malukus/Moluccas Indonesia: Asia/Makassar (WITA) – Borneo (east, south); Sulawesi/Celebes, Bali, Nusa Tengarra; Timor (west) Indonesia: Asia/Pontianak (WIB) – Borneo (west, central) Indonesia: Asia/Jakarta (WIB) – Java, Sumatra 

We need to store both to make sure people who fill in "Isle of Man, Europe/London" aren't shown "you selected Britain, Europe/London" when they revisit a settings page.