Geographical boundaries for the continental US tz zones

Robert Elz kre at munnari.OZ.AU
Thu May 31 15:27:16 UTC 2007

    Date:        Wed, 30 May 2007 22:55:25 -0700
    From:        Eric Muller <emuller at>
    Message-ID:  <465E634D.2080301 at>

  | I am trying to figure out the geographical extent of the 19 continental 
  | US timezones defined by tz.

Sorry, I can't help with that, but your question is a fairly common kind of
one - we keep having people attempt to draw maps from the timezone data.

I don't believe that it is really particularly suited for that, nor that
it should be.

The aims of this project are to identify all of the distinct timezones that
exist, as best we can - it isn't part of our aim to specify just who is
supposed to use each of those timezones, that's what the local legislature
or executive administration (or whatever) does - or attempts to do, usually
out near what you'd like to be a nice clear boundary between zones there's
actually lots of ambiguity.

This project doesn't care - as long as each individual user can decide
"my local time is always the same as that in New York city" (or wherever)
then they can select data that is going to be correct for them.   It is
irrelevant whether their neighbours use the same zone, which side of some
boundary line they're on, or anything else like that.

This all means that we don't much care where the boundaries are and
there's no reason that we should, even if there really are nice fixed
boundaries.  What is more important here is when someone discovers that
some region uses a mapping from UTC onto wallclock time that isn't the
same as any that we have, or when one of the existing ones changes its
rules.   The actual set of people that any of this applies to isn't
so important (as long as it is more than 0, or it isn't worth distributing).

None of this means that what you're doing isn't useful, and if and when
you find errors in the zones, or the comments about the zones I'm sure
they'll be corrected.   It also doesn't mean that there aren't people on
this list who can answer some or all of your questions - nor that you
shouldn't have asked them.  I'm just trying to discourage any (more) bending
of the timezone data towards the needs of map makers - that isn't the


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