pre-1970time zones

[aloistr]

Hello
you may now that TZ zones are only aiming to be good after 1970. If one wants correct tme zone information before 1970, additonal zones are needed. Actually up to 2500 extra zones. The worst are some US states and some Canada provinces, which gave authority up to 1967 to local counties or communes to decide about following daylight savin time or not.
If one leaves out these US states and Canada provinces, I have so far define 239 extra zones.
Question: how can one go about defining boundary lines for these?
The original TZ zones remain, but become much smaller. For example in Germany, in addition to Europe/Berlin appear these extra zones
Zone Europe/Germany/Mannheim 0:33:56 - LMT 1891 Mar 15 #azn=133
Zone Europe/Germany/Munich 0:46:12 - LMT 1891 Mar 15 # azn=134
Zone Europe/Germany/Stuttgart 0:36:44 - LMT 1891 Mar 15 0:00 #azn=135
Zone Europe/Germany/Frankfurt 0:34:40 - LMT 1893 Apr #azn=136
Zone Europe/Germany/Mainz 0:33:44 - LMT 1891 Mar 15 #azn=138
Zone Europe/Germany/Cologne 0:27:56 - LMT 1893 Apr # azn=139
Zone Europe/Germany/Breslau 1:08:00 - LMT 1893 Apr 1 # azn=140
Zone Europe/Germany/Danzig 1:14:40 - LMT 1893 Apr 1 # azn=141
Zone Europe/Germany/Saarbrucken 00:33:44 - LMT 1891 Mar 15 # azn=143
Zone Europe/Germany/Montabaur 0:33:04 - LMT 1891 Mar 15 # azn=144

[evansiroky]

Seems like an interesting idea. I wouldn't be able to work on this on my own, so would need help from whoever is interested in working on this.

[1ec5]

These historically-oriented zones would be far too controversial to map in OpenStreetMap directly. It would be better to maintain heuristics in this repository or Wikidata to query boundaries from OSM and/or OHM. This will require some cleanup on the Wikidata side.

Note that the backzone file doesn’t aim to be complete. From what I’ve seen in North America, it’s got huge gaps in it between the introduction of standard time and 1970.