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What is the origin of the time zones that come with Windows? For the sake of example, I shall list some here (from using PowerShell, but the info is not .NET-specific):
PS C:\Users> [TimeZoneInfo]::FindSystemTimeZoneById("W. Europe Standard Time")
Id : W. Europe Standard Time
HasIanaId : False
DisplayName : (UTC+01:00) Amsterdam, Berlin, Bern, Rome, Stockholm, Vienna
StandardName : W. Europe Standard Time
DaylightName : W. Europe Daylight Time
BaseUtcOffset : 01:00:00
SupportsDaylightSavingTime : True
PS C:\Users> [TimeZoneInfo]::FindSystemTimeZoneById("Central Europe Standard Time")
Id : Central Europe Standard Time
HasIanaId : False
DisplayName : (UTC+01:00) Belgrade, Bratislava, Budapest, Ljubljana, Prague
StandardName : Central Europe Standard Time
DaylightName : Central Europe Daylight Time
BaseUtcOffset : 01:00:00
SupportsDaylightSavingTime : True
PS C:\Users> [TimeZoneInfo]::FindSystemTimeZoneById("Romance Standard Time")
Id : Romance Standard Time
HasIanaId : False
DisplayName : (UTC+01:00) Brussels, Copenhagen, Madrid, Paris
StandardName : Romance Standard Time
DaylightName : Romance Daylight Time
BaseUtcOffset : 01:00:00
SupportsDaylightSavingTime : True
PS C:\Users> [TimeZoneInfo]::FindSystemTimeZoneById("Central European Standard Time")
Id : Central European Standard Time
HasIanaId : False
DisplayName : (UTC+01:00) Sarajevo, Skopje, Warsaw, Zagreb
StandardName : Central European Standard Time
DaylightName : Central European Daylight Time
BaseUtcOffset : 01:00:00
SupportsDaylightSavingTime : True
All these four entries ("W. Europe Standard Time", "Central Europe Standard Time", "Romance Standard Time", "Central European Standard Time"
) are essentially equivalent, but confusing in several ways. Here are some examples:
- The name W. Europe Standard Time is often used for UTC±00:00 used in Lisbon, London etc., so where does the name come from?
- The word Romance in the third one is curious. One city mentioned (Copenhagen) uses a non-Romance language (Danish, a Germanic language), while a city with clearly Romance association (Rome, from the name of which Romance is derived) is in another entry.
- There is no meaning to the groups. Like why are Amsterdam and Brussels in different groups? And why does Stockholm go together with Amsterdam while Copenhagen goes with Brussels?
- If you are in Oslo (not mentioned), would you pick Copenhagen or Stockholm?
- The names Central Europe Standard Time and Central European Standard Time are very similar? Why is Zagreb not grouped together with Ljubljana; the cities of the Balkans are completely randomly distributed between the two groups?
So my main question is, what is the explanation for these groups? Is there a map from tz database entries to the groups used by Windows?
FindSystemTimeZoneById
. So that gives a map, and I can reveal that[System.TimeZoneInfo]::FindSystemTimeZoneById("Europe/Oslo").DisplayName
gives"(UTC+01:00) Amsterdam, Berlin, Bern, Rome, Stockholm, Vienna"
. My question about where the Windows entries come from still stands.