The naive approach to time zones– one I’ve seen in way too much code– is that a time zone is defined by the difference between local time and UTC. Their time zone data helpfully includes a file named zone.tab that maps time zone names to other details about the zone. This file is a simple tab-delimited file that includes the time zone name, an ISO 3166 two-letter country code, and a latitude/longitude coordinate for the city that defines the zone.