I have never had an opportunity to deploy this tool, but here's a program for generating a TZ shapefile from OpenStreetMap data: https://github.com/evansiroky/

I have never had an opportunity to deploy this tool, but here's a program for generating a TZ shapefile from OpenStreetMap data: https://github.com/evansiroky/timezone-boundary-builder https://github.com/evansiroky/timezone-boundary-builder In principle a calendar program could use its output to perform GIS lookups of locations then use the tzinfo DB to get the correct timezone at the given location and specified time.