[tz] efele.net/tz maps updated

Eric Muller eric.muller at efele.net
Sun Nov 29 17:31:21 UTC 2015

On 11/29/2015 12:28 AM, L. David Baron wrote:
> On Sunday 2015-11-08 10:31 -0800, Eric Muller wrote:
>> I have updated the efele.net/tz maps (http://efele.net/maps/tz/) to be in
>> sync with TZ 2015g. The new zones:
> It's great to see this updated.


> A few comments on the data:
>   (1) There are a few shapes in the maps that correspond to zones
>       that are now links.

I started the maps while TZ still had a policy that a timezone would be 
"contained" in a political entity. When the great zone unification 
happened, I was faced with the choice to apply or not that unification 
to the maps. As it was a bit unclear where TZ would end up, and because 
it's easier to merge the shapes for those zones (it only takes data in 
TZ) than to split them (had I done the unification), I elected to retain 
as many zones as possible (see my message to this list on July 26, 
2014). I took all the zone names that existed, rejected names like 
Etc/GMT+10, rejected names that are obviously aliases for the same 
geographical extent (eg Africa/Asmera, retaining Africa/Asmara), and 
kept all the others.

It should be a trivial matter to take any equivalence relation on the 
zones and produce a map that has a single shape for each class. The 
equivalence relation could be "zones are linked", or "zones have the 
same local time over a given period of time".

>   (2) I noticed that the map uses the Sudanese claim for the border
>       between Egypt and Sudan.

>   (3) When overlaying on other maps, I notice that the edges of the
>       Aral sea are rather out-of-date.

Obviously, I could not come up with the TZ boundaries ex-nihilo. Because 
they mostly correspond to land and administrative boundaries, I had to 
start from an existing map that contains those boundaries. I also wanted 
a worldwide map, and the result to be as free as possible. The only/best 
dataset I could find is VMAP0. Unfortunately, that's a relatively old 
dataset and it has not been updated to account for changes in 
administrative boundaries. Another case is the Saudi Arabia/Yemen boundary.

Arguably, I could try to fix those situations by injecting "better" 
data. Besides the inherent difficulty of that exercise (where do I get 
accurate data? how do I stitch it in?), it would also mean that my map 
could no longer be seen as an additional layer of the VMAP0 dataset.

I did the best I could to facilitate the creation of a timezone map 
using another base dataset, by providing a logical description of the 
zones, and by publishing the script that relies mostly on FIPS 10-4 

May be it's time to move the effort to, e.g., OpenStreetMap?

> (I've been playing with using the data to draw a "live" timezone map
> on the Web,

It would be cool to have a dual slider to select a time span for the 
map. Seeing a timezone as a function relating utc time and local time 
(over time), you can restrict those functions to a domain via the 
slider, and distinguish on the map only those functions which are distinct.


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