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Hancock, David (dhancock) wrote:
<blockquote cite="mid:C4F2720D.34EB7%25dhancock@arinc.com" type="cite">
<title>Timezones as shapefiles (was: Re: Chinese timezones 1970)</title>
<font face="Verdana, Helvetica, Arial"><span style="font-size: 12px;">Our
group is relatively new to the tzdb and very new to GIS, but we do know
that having timezone boundaries as shapefiles would be very useful.<br>
<br>
Is there a comprehensive source for timezones as shapefiles? It looks
like a tremendous amount of work to do them--just wondering if it's all
(or mostly) done already.<br>
<br>
</span></font></blockquote>
<br>
To my knowledge, there is not yet a publicly available shapefile that
covers all the tz timezones, but there are shapefiles that cover
"modern" time zones.<br>
<br>
As I alluded earlier, I am working on such a shapefile. There are three
main difficulties:<br>
<br>
- understand what a tz timezone is a about (e.g. Asia/Samarkand vs.
Asia/Tashkent) in logical terms, typically in terms of administrative
divisions.<br>
<br>
- locate source GIS material for administrative divisions, with the
appropriate traceability and distribution rights. Traceability is
important: anybody can put together a shapefile, but it does not do
much good if we don't know the quality of the data (whatever it may
be), etc. And of course distribution rights probably matter to some
users.<br>
<br>
- put everything together by a process that is automated enough so that
new versions can be created easily, as new tz timezones are created,
source material is corrected or the procedure itself is debugged.<br>
<br>
Fortunately, the VMAP0 polbnda layer provides most of the
administrative divisions we need, is a known quantity and has the most
liberal distribution rights I have found. I have already converted that
layer to a usable shapefile (<a class="moz-txt-link-freetext" href="http://efele.net/maps/vmap0/polbnda/">http://efele.net/maps/vmap0/polbnda/</a>). I
also established the mapping to FIPS 10-4 codes at
<a class="moz-txt-link-freetext" href="http://efele.net/maps/fips-10/">http://efele.net/maps/fips-10/</a> (the VMAP0 data only has names, which
are a pain to manipulate). That still leaves a few cases where we needs
boundaries not present in VMAP0:<br>
<br>
- US: I have built a shapefile using various sources at
<a class="moz-txt-link-freetext" href="http://efele.net/maps/tz/us/">http://efele.net/maps/tz/us/</a>. <br>
- Canada: I have created a first cut that deals with all but a few
little zones<br>
- China: I posted that one yesterday at <a class="moz-txt-link-freetext" href="http://efele.net/maps/tz/ch/">http://efele.net/maps/tz/ch/</a><br>
- Russia: I have a shapefile for that one, built from the map at
<a class="moz-txt-link-freetext" href="http://wagda.lib.washington.edu/DATA/geography/world/russia/download.html">http://wagda.lib.washington.edu/DATA/geography/world/russia/download.html</a><br>
- Brazil: that one is easy (using the VMAP0 layer for rivers, and a bit
of geometry)<br>
- Australia: currently working on that one, does not seem too
problematic<br>
- a few tz timezones are easy to describe in geometric terms (e.g.
isolating the Kwajalein atoll)<br>
<br>
I also have a scheme to put everything back together with the VMAP0
data, and obtain a single shapefile for the world. As soon as I have
Australia in good enough shape, I'll publish it, along with the
procedure and all the source material I used; I hope to do that within
a week or two. Of course, there will be some bugs, which I will be
happy to fix.<br>
<br>
Eric.<br>
<br>
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