Geographical boundaries for the continental US tz zones
emuller at adobe.com
Thu May 31 05:55:25 UTC 2007
I am trying to figure out the geographical extent of the 19 continental
US timezones defined by tz. Because my goal is ultimately to create a
freely available digital map, I would like to get definitions in terms
existing, freely available digital maps, and the ones at
nationalatlas.gov seem appropriate. Specifically, I plan to use
countyp020 (county boundaries 2001), statesp020 (states) and timeznp020
(time zones) [see below for more details on those maps]. I tried to
translate the comments in the "northamerica" file in terms of operations
on the elements of those three maps, but I have a few questions/comments.
1. I would think that America/Boise, America/Denver and America/Phoenix
together correspond exactly to the Mountain time zone of timeznp020.
However, the later includes the southern quarter of Idaho County, Idaho,
while northamerica suggests that this county is entirely in
America/Pacific. Who is right?
2. The description of America/Denver includes "far eastern Oregon", and
the description of America/Boise includes "eastern Oregon". Comparing
with timeznp020, I suspect that America/Denver should not include "far
eastern Oregon". (and if timeznp020 is right, "eastern Oregon" could be
better described as "most of Malheur County, Oregon").
3. What does America/Indiana/Indianapolis cover? Is it all the counties
of Indiana not listed in any of the other zones?
4. The overall description of Indiana includes:
# - Daviess, Dubois, Knox, Martin, Perry, and Pulaski counties
# have been like America/Indiana/Vincennes.
# - Crawford, Pike, Starke, and Switzerland counties have their own time
# histories as noted below.
However, it seems that Pulaski now has it own zone
(America/Indiana/Winamac), so it should probably be moved from the first
to the second bullet in the quote above.
5. The description of America/Indiana/Marengo is that it covers the
eastern part of Crawford County. How is that county divided, and in
which zone does the western part fall?
6. What part of Kentucky goes in America/Kentucky/Louisville?
At this point, I am not trying to handle border towns such as West
Wendover, mostly because I have no idea of where to find a boundary for
such towns. Any suggestion on what to do for those cases is welcome.
For those of you who are curious about the content of the maps cited
above: you can download them from
<http://nationalatlas.gov/atlasftp.html> and visualize them using
standard GIS tools (I use the freely available OpenJUMP and uDig).
Alternatively, I have created a KML version of timeznp020 (using
org2ogr) and placed it at <http://efele.net/timeznp020.zip> (4MB, 15MB
uncompressed); you can visualize it in Google Earth (File->Open); I
assume that the built-in 1st level and 2nd level admin regions (under
"borders") are close enough to statesp020 and countyp020.
Below is my current recipe to build my map in terms of operations in the
source maps. Comments welcome.
timeznp020/(Mountain & no DST)
statesp020/(Idaho+Oregon) intersected with timeznp020/Mountain
countyp020/(Oliver County, North Dakota)
countyp020/(Morton County, North Dakota)
countyp020/(Crawford County, Indiana)
// should only be the eastern part of Crawford County? where is the
// limit? where does the western part go?
countyp020/(Daviess, Dubois, Knox, Martin, and Perry Counties, Indiana)
countyp020/(Pike County, Indiana)
countyp020/(Starke County, Indiana)
countyp020/(Pulaski County, Indiana)
countyp020/(Switzerland County, Indiana)
countyp020/(Clark, Floyd, and Harrison counties, Indiana)
// what part of Kentucky is in this zone?
countyp020/(Wayne County, Kentucky)
// statesp020/Indiana minus what is already covered above minus
// Dearborn and Ohio County (they are in America/New_York) and
// minus Gibson, Jasper, Lake, LaPorte, Newton, Porter, Posey,
// Spencer, Vanderburgh,
// and Warrick counties (they are in America/Chicago)
countyp020/(Dickinson, Gogebic, Iron, and Menominee Counties, Michigan)
statesp020/Michigan minus what is already covered above
timeznp020/Pacific minus what is already covered above
timeznp020/Mountain minus what is already covered above
timeznp020/Central minus what is already covered above
timeznp020/Eastern minus what is already covered above
More information about the tz