Hancock, David (dhancock) wrote:
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.
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.
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. As I alluded earlier, I am working on such a shapefile. There are three main difficulties: - understand what a tz timezone is a about (e.g. Asia/Samarkand vs. Asia/Tashkent) in logical terms, typically in terms of administrative divisions. - 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. - 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. 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 (http://efele.net/maps/vmap0/polbnda/). I also established the mapping to FIPS 10-4 codes at http://efele.net/maps/fips-10/ (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: - US: I have built a shapefile using various sources at http://efele.net/maps/tz/us/. - Canada: I have created a first cut that deals with all but a few little zones - China: I posted that one yesterday at http://efele.net/maps/tz/ch/ - Russia: I have a shapefile for that one, built from the map at http://wagda.lib.washington.edu/DATA/geography/world/russia/download.html - Brazil: that one is easy (using the VMAP0 layer for rivers, and a bit of geometry) - Australia: currently working on that one, does not seem too problematic - a few tz timezones are easy to describe in geometric terms (e.g. isolating the Kwajalein atoll) 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. Eric.