Zone & HourData sources and methodology
City catalogue
The 450-city search catalogue is derived from the GeoNames cities15000 extract and countryInfo data. GeoNames data is licensed under CC BY 4.0. Attribution: GeoNames.
Changes made for this site: included 190 Alpha–Gamma centers from the GaWC 2024 World Cities classification, selected national capitals present in the extract, retained a curated list of business and travel hubs, filled the remaining places by population, normalized URL slugs and shortened aliases for search. Some familiar English display names are explicitly mapped. Duplicate place names receive distinct slugs.
GaWC ranks nodes in the world-city network using advanced producer-service firms. We use its classification to prioritize search coverage, not to calculate local times or imply that unranked cities are unimportant. Place names and time zones still come from GeoNames.
Population is used for catalogue selection and search ordering, not presented as a current population estimate. The source script caches downloaded extracts and can regenerate the catalogue without a paid account.
Country flags
Small flag SVGs are hosted locally from flag-iconsv7.3.2, licensed under the MIT license. They identify the country listed beside each city; they do not represent the city itself.
Time-zone rules
The IANA Time Zone Database provides the rule model used by modern browser and operating-system implementations. Runtime calculations use the user’s installed Intl.DateTimeFormat data. Static tables use the build runtime’s installed data. This website does not bundle a separate tz database or claim it has the newest version on every device.
Editorial page selection
The initial city and corridor collection represents common international scheduling scenarios: major business hubs, regional connections, fractional offsets and seasonal-clock edge cases. These are editorial choices, not claims of independently measured keyword volume. Expansion should be guided by actual search impressions and user needs.
Published clock-change guidance
- NIST: US daylight-saving rules
- UK government: clock changes
- NSW government: daylight saving
- New Zealand government: daylight saving
- BIPM: international time metrology
Reporting corrections
For city metadata, retain the GeoNames ID when proposing a change. For time rules, include the full date, city identifier, expected offset and the relevant official notice. See contact information.