Geographical boundaries for the continental US tz zones

Paul Eggert eggert at CS.UCLA.EDU
Wed Jul 18 07:41:28 UTC 2007

Jesper Norgaard Welen tried to send the following email to the list on
July 1, but apparently didn't get through.  I am enclosing it in the
hopes that it does get through this time.

From: Jesper Norgaard Welen [mailto:jnorgard at] 
Sent: Domingo, 01 de Julio de 2007 16:15
To: 'tz at'
Cc: 'emuller at'
Subject: RE: Geographical boundaries for the continental US tz zones

Hello, Eric Muller

I send my comments to your US timezone map directly to the TZ list since I
think it could be of common interest in the list and also to urge members to
send comments where appropriate.
My newest map for World Time Explorer you can download from

* Navajo/Hopi reservations
There is an important Hopi population that you have not included around
Latitude 36.14 Longitude -109.40 that I would recommend you to include (see
WTE map)

* Nevada on Idaho time
The city Jackpot in Nevada (and several others like Owyhee and Mountain
city) are on Idaho south time, or Denver time if you will. I have included
it in a 25 km broad strip of northern Elko county, however just based on
common sense when there were cities 12 km below the border that were on
Denver time, and I would not expect their time to stop 100 meters outside
the city boundary, but note that it is arbitrary, and quite possibly not
quite 25 km. Jackpot itself is quite close to the border to Idaho.

* Idaho county split (Idaho state)
I have a northern and southern part of Idaho county, which I got from
another timezone map (possibly Manifold map). This indicates that the
southern part of Idaho county is on America/Boise time while the northern
part is on America/Los_Angeles. Note that this is *not* documented in the tz
database - I am still a bit ambivalent which one to believe. If you want
pure tz database functionality, the timezone border should be a little
further south.

* Alaska
I have the same doubts as you. However, I have implemented a solution,
however arbitrary it is, seems much better than just putting Juneau for all
of Alaska. The Nome area is small, while most of northwestern Alaska is set
to Anchorage time. Then there is a Yakutat area and a Juneau area. They are
all based on counties in this area. Comments are welcome.

* America/Kentucky/Louisville
This city belongs to Jefferson county of Kentucky, so I just assumed that
this would comprise the Louisville timezone - however tz database needs to
describe this - and include more counties if there are more. It just states
the vague "part of Kentucky".

* Sioux county North Dakota
Tz database states "part of Sioux county" and that is exactly what you have
included, splitting it around Latitude 46 Longitude -101.34. Where did you
get shis from? I have included all Sioux county being on same time, but that
most be wrong.

* Cherry county Nebraska
I see you have a different, more detailed split of Cherry county than mine.
Where did you get this from?

* Morgan county, Tennessee
I recently discovered that this county is on CST/CDT, and included this in
the western part of Tennesse. It's around Latitude 36.07 Longitude -84.56

* Alabama
Note that (parts of) Chambers, Lee and Russell counties should be on
America/New_York time, not on America/Chicago time.

* Culberson county, Texas
Note that the parts of this county including Nickel creek and Pine Springs
are on America/Denver time.

- Jesper Nørgaard Welen

-----Original Message-----
From: Eric Muller [mailto:emuller at] 
Sent: Domingo, 01 de Julio de 2007 12:07
To: tz at
Subject: Re: Geographical boundaries for the continental US tz zones

I have completed a first version of a map of the TZ timezones in the US.
It is available as a shapefile at <>.

Comments welcome,

More information about the tz mailing list