[tz] Recent conversions of zones to aliases
lester at lsces.co.uk
Fri Oct 3 22:01:25 UTC 2014
On 03/10/14 21:37, Guy Harris wrote:
> On Oct 3, 2014, at 12:58 PM, Lester Caine <lester at lsces.co.uk> wrote:
>> On 03/10/14 20:38, Guy Harris wrote:
>>> 1) have a database to map locations to tzids;
>> This is what geonames currently provides, but using the 'full' TSID list
>> from TZ currently.
> So presumably by "location" you mean "something with an entry in the GeoNames database":
> rather than "a longitude+latitude".
> In either case, for any given location, the tzid and longitude+latitude can be determined, with the help of the appropriate databases.
Of cause one needs to add in changes in names over time ... us to
complete the picture.
>> What is missing is the gap between what is valid data on TZ and the
>> actual location based history.
>> For example when Oxford switched from Oxford time to Europe/London and
>> in parallel when railway time was used at the station. Basically how to
>> add this historic data to the time offset system.
> So how was "Oxford time" defined? Was there a specified offset, or was it just, for example, mean solar time at some location in Oxford, or mean time wherever you happened to be in Oxford?
Many towns set their main clocks to local mean solar time.
Initial confusion was against railway time and then against 'GMT'. Some
clocks gained an extra minute hand and the Tom Tower in Oxford was one
of those clocks.
> Note that the GeoNames site says, "The GeoNames geographical database covers all countries and contains over eight million placenames that are available for download free of charge.", so if every location in the GeoNames database has a separate offset, that's unlikely ever to be in the tz database.
> The tz database is not, and should not ever be, the place to go for information about solar-time-based local time. A case *might* be made for local times that aren't solar-time-based but that weren't standardized in the "standard time" sense, if any such local times existed.
And that timezones have a starting date and time is sort of recorded in
the TZ database, and it is one of those elements where the accuracy of
dates may be suspect but where we have that information it should be
That this requires additional ID's is the problem here, and where a
clear distinction between tz data rule set designations and location
rule sets needs to be drawn. My objection still and one that comes even
more important in the context of tzdist is that truncated data sets
should be truncated at the point that a common rule is identified, not
pretending that the earlier data of one set applies to all of them.
I do now feel that TZ is NOT an appropriate home for all of this
intermediate data that is now starting to emerge from the increasing
scanning of historic documents. We do need somewhere where this material
can be recorded and used as a publisher of tzdist data that can be used
reliably prior to 1970.
Lester Caine - G8HFL
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