[Tagging] Mapping time zones as geometries (relations)

Rafael Avila Coya ravilacoya at gmail.com
Mon Mar 6 00:57:22 UTC 2017


I generally agree with your view.

The wiki [1] already says: "An effective way to tag timezone information 
is to add it to administration boundaries of countries or in the case of 
larger countries smaller administrative boundaries such as states and 
territories. (Do not create stand-alone boundaries for time zones in OSM.)"

I would keep the timezone data in OSM, but doing it that way: adding the 
timezone tag to boundary relations (most countries, some states and few 
level-6), except for those very rare cases it doesn't follow an admin 
boundary.

Cheers,

Rafael.

[1] http://wiki.openstreetmap.org/wiki/Key:timezone

On 06/03/17 01:30, Frederik Ramm wrote:
> Hi,
>
>    I would like to start a discussion about the mapping of time zones.
>
> There are currently 80 relations in OSM tagged as boundary=timezone
> using between them over 10,000 ways.
>
> I think that mapping these time zones as geometries has several issues:
>
> 1. It introduces yet another un-observable object type into OSM. When I
> asked about the source of the data, one person quipped "well you can
> observe it on a local clock", but the people adding time zone boundaries
> don't seem to actually do that - they copy the information from somewhere.
>
> 2. It is for the most part unnecessary noise; almost all time zone
> boundaries run along administrative boundaries, so you could just add a
> timezone tag to the administrative entity instead of mapping a whole
> separate geometry.
>
> 3. It complicates editing; anyone touching one of the aforementioned
> 10,000 ways (which are for the most part also used by admin boundaries)
> will be confronted with the time zone relation and will have to decide
> what to do with it.
>
> 4. It creates very large polygons that may be difficult to edit.
>
> Here's a list of time zones currently mapped in OSM (with relation ID)
>
> 3563652 Московское время
> 3563678 Екатеринбургское время
> 3563726 Красноярское время
> 3563727 Омское время
> 3563885 Иркутское время
> 3563886 Якутское время
> 3563937 Владивостокское время
> 4297465 Самарское время
> 6426325 Cherry County - Chicago TZ part
> 6426796 Idaho Denver TZ part
> 6426797 Idaho Los Angeles TZ part
> 6428675 Alaska - Timezone America/Adak
> 6428690 Alaska - Timezone America/Anchorage
> 6428730 Alaska - Timezone America/Yakutat
> 6428802 Alaska - Timezone America/Juneau
> 6428803 Alaska - Timezone America/Sitka
> 6428944 Canada - Timezone America/Pangnirtung
> 6430296 Malaysia - Kuala Lumpur Timezone
> 6430370 Kiribati - Kiritimati timezone
> 6430371 Kiribati - Tarava timezone
> 6430484 Greenland - timezone America/Danmarkshavn area
> 6430503 Greenland - timezone America/Thule area
> 6430514 Greenland - timezone America/GodThab area
> 6430515 Greenland - timezone America/Scoresbysund area
> 6430658 Хандыгское время
> 6440860 America/Tijuana Timezone
> 6440942 America/Merida Timezone
> 6440955 America/Cancun Timezone
> 6440975 America/Bahia_Banderas Timezone
> 6441066 America/Mazatlan Timezone
> 6442501 America/Mexico_City Timezone
> 6442514 America/Santa_Isabel Timezone
> 6442531 America/Hermosillo Timezone
> 6442686 America/Matamoros Timezone
> 6442687 America/Ojinaga Timezone
> 6442693 America/Chihuahua Timezone
> 6442726 America/Monterrey Timezone
> 6442820 America/Edmonton Timezone part
> 6442821 America/Regina Timezone
> 6442822 America/Winnipeg Timezone part
> 6445625 America/Eirunepe Timezone
> 6445626 America/Manaus Timezone
> 6445682 America/Belem Timezone
> 6445683 America/Santarem Timezone
> 6445860 Asia/Dushanbe Timezone part
> 6446092 Arizona - America/Phoenix Timezone
> 6446108 America/Atikokan Timezone
> 6446109 America/Winnipeg Timezone
> 6446170 America/Cambridge_Bay Timezone
> 6446189 America/Rankin_Inlet Timezone
> 6446190 America/Resolute Timezone
> 6451096 Atlantic/Azores Timezone
> 6451097 Atlantic/Madeira Timezone
> 6451098 Europe/Lisbon Timezone
> 6451458 America/Coral_Harbour Timezone
> 6451459 America/Iqaluit Timezone
> 6483867 Ontario - America/Toronto Timezone
> 6483978 America/Creston Timezone
> 6483979 America/Dawson_Creek Timezone
> 6483980 America/Edmonton Timezone
> 6483981 America/Vancouver Timezone
> 6485969 Asia/Sakhalin Timezone
> 6491030 America/Argentina/Buenos_Aires Timezone
> 6491031 America/Argentina/Catamarca Timezone
> 6491032 America/Argentina/Rio_Gallegos Timezone
> 6491033 America/Argentina/Salta Timezone
> 6491034 America/Argentina/Ushuaia Timezone
> 6491133 Atlantic/Canary Timezone
> 6491134 Europe/Madrid Timezone
> 6491494 America/Chicago Timezone
> 6496417 America/New_York Timezone
> 6496587 America/Indiana/Indianapolis Timezone
> 6496665 America/Boise Timezone
> 6496694 America/Los_Angeles Timezone
> 6498476 America/Menominee Timezone
> 6498563 America/Detroit Timezone
> 6498592 America/Nipigon Timezone
> 6498593 America/Thunder_Bay Timezone
> 6594626 Магаданское время
> 6594635 Камчатское время
>
> And here's them in a map:
>
> http://www.remote.org/frederik/tmp/tz.jpg
>
> Now when you overlay the administrative boundaries on levels 2 and 4,
> only very few lines remain:
>
> http://www.remote.org/frederik/tmp/tz4.jpg
>
> And when you go up to admin level 6:
>
> http://www.remote.org/frederik/tmp/tz6.jpg
>
> Assuming that these boundaries are actually correct, the only places in
> which time zone boundaries don't follow admin boundaries are:
>
> * In South America, the Western boundary of the Manaus timezone and the
> Eastern boundary of the Santarem timezone;
>
> * In North America, the line between the Hermosillo and Santa Isabel
> timezones, the Phoenix timezone, a small part of the boundary between
> the Los Angeles and Boise time zones in Malheur county, the Chicago
> Timezone in Cherry County, a piece of the Los Angeles timezone in Idaho,
> the line between Vancouver and Dawson Creek respectively Creston
> timezones, two incursions into the Regina timezone for Edmonton and
> Winnipeg, two micro timezones called Nipigon and Thunder Bay, as well as
> the Iqaluit and Rankin Inlet timezones far North. (Strangely, around
> Alaske the timezone boundary seems to include a few miles of water that
> are not included in the admin boundary - a quirk in mapping or a quirk
> in time zone definitions?)
>
> As you can see in the images, these lines make up just a fraction of
> time zone boundaries (and it is quite possible that some of these just
> shine up because the matching admin6 boundaries haven't yet been mapped).
>
> I fear that the presence of *some* time zone relations will entice
> people to map even more of them, unnecessarily introducing extra
> geometries into our database when you could easily build time zone
> geometries by either (a) keeping an external database that says "Time
> Zone X consists of the following administrative units" and then
> collecting the units from OSM, or (b) adding a time zone tag to
> adminsitrative entities in OSM - namely, the highest entitiy that still
> has the same time zone which will often be a whole country, sometimes an
> admin-4 entity and very rarely an admin-6 entity.
>
> If there are really some time zone bits and pieces that don't follow
> admin boudnaries (maybe they're marked with signs on the ground
> "caution, wind back your clock all ye who pass here"?) then maybe those
> few bits can be mapped as individual objects... but please, don't
> inflate OSM with time zone geometries just because "it's easier to
> consume that way" (which is the gist from a discussion I had with a time
> zone mapper).
>
> I am worried because with the same reasoning, you could start mapping
> things like "states that have signed up to the XYZ treaty", "states in
> which XYZ is legal/illegal", or anything else. It's a slippery slope,
> and *if* time zones are mapped in OSM at all, I'd rather not have them
> mapped as giant geomtries in their own right, but as properties.
>
> I have recently deleted a few time zone relations in the US and,
> grudgingly, reinstated them because I had to accept that a prior
> discussion was called for. (Changeset discussion here
> https://www.openstreetmap.org/changeset/45644359), and I also requested
> the deletion of
> http://wiki.openstreetmap.org/wiki/Tag:boundary%3Dtimezone which
> prompted verdy_p to write a small novel on the talk page there.
>
> I find the subject of time zones hugely interesting and seeing the
> quirks mapped above has already sent me on a journey reading up on the
> details, but I still think that the mapping of time zones as geometries
> should be discouraged in OSM.
>
> What do you think?
>
> Bye
> Frederik
>



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