About ZoneHop

Two modes

ZoneHop has two ways of showing the same list of cities, and the switch at the end of the header moves between them. They answer different questions, so they keep different clocks.

Schedule is for coordinating a meeting across several time zones. It lays one 24-hour window across every city at once, scores every quarter hour against ordinary business hours and lets you move to any date — so an hour next Tuesday can be settled before anybody has to be asked about it. It runs on the instant you pick.

Map is for monitoring rather than planning: the world under live daylight, with a clock for every city on your list underneath it. It is meant for a watch floor, an operations floor or a command centre — anywhere the standing question is what time it is, right now, in all of these places. It runs on the real clock, takes no date, and redraws itself as the Earth turns.

How the Schedule works

ZoneHop lays one 24-hour window across every city you add. The window runs midnight to midnight in the first city on the list, and every other row shows that same stretch of real time seen from somewhere else — so a vertical line through the board is a single instant, everywhere at once.

Drag the marker to a time and the board tells you what the time is in each city. It is built for arranging a meeting next Tuesday; for what time it is right now, the Map is the view that answers that.

More than a converter

Knowing that 15:00 in Berlin is 06:00 in San Francisco is the easy part. The question you actually have is whether anyone should be expected to take a call then.

Every quarter hour is scored against standard business hours: 09:00 to 17:00 local is prime, 07:00 to 09:00 and 17:00 to 21:00 are workable if there is a reason, and the rest is somebody’s night. The curve above the rows adds those scores across your whole list, so its peaks are the hours the group genuinely shares. “Best hour” jumps the marker to the highest one.

There is no setup, there are no per-person calendars and there are no accounts. The tiers are the same for everyone, which is what makes the board readable at a glance.

Daylight, not decoration

The coloured band on each row is that city’s real daylight for the date you picked: solar elevation computed from its latitude and longitude, so day length, the direction the light moves and the width of twilight are all true. Reykjavík in June and Reykjavík in December do not look alike, because they are not.

It is there because a number tells you 06:00 and a picture tells you dark.

The Map shades the whole globe with the same calculation, so the edge of night there and the twilight on a row are one fact seen from two directions.

Built to be read anywhere

ZoneHop was designed from the start for people scattered across the world, so it speaks six languages: English, Spanish, French, Chinese, Hindi and Portuguese. It opens in whichever of them your browser asks for, and you can change it at any time from the globe in the header.

Dates, clock formats, month and weekday names, the day the week starts on and country names all come from your browser’s own internationalisation data rather than from a table we keep by hand. They follow the conventions of the language you chose instead of a translation of ours.

The board also opens on your own city, worked out from your device’s time zone, because the first row is the frame everything else is read against.

Where the numbers come from

• Time zones and daylight saving — your browser’s copy of the IANA time zone database, read through the standard Intl interface. That is the same data your operating system uses and is kept current by system updates, which is why an unusual offset like Kathmandu’s UTC+05:45, or a rule that changed last year, lands correctly without us shipping anything.
• Sunrise, sunset and twilight — solar position computed with the approximation published by the NOAA Global Monitoring Laboratory, evaluated for each city’s coordinates. It is good to about a minute for this purpose and makes no allowance for altitude or local terrain.
• Cities — a hand-curated list of 231 cities across 151 time zones, each with coordinates and an approximate metropolitan population. Population is used only to rank search results and to choose a sensible stand-in when your exact zone is not on the list.
• Coastlines — Natural Earth 1:110m land, which is in the public domain. It was reprojected and simplified once, before the page was built, and ships inside it: the Map draws no tiles and asks nobody for anything.
• Country and language names — the CLDR data already built into your browser.

None of the timekeeping data is fetched at runtime. The whole dataset ships with the page, which is why the board keeps working with the network off.

What it does not know

Public holidays, school runs, Ramadan, the colleague who starts at seven and is gone by three. The tiers are a reasonable default, not a claim about anyone’s actual day — treat the board as a shortlist and confirm with the people involved.

City names stay in their usual written form rather than being translated, because there is no reliable source for translated place names and a hand-kept table across six languages would quietly rot. Search accepts common local spellings.

Historic dates work, but the further back you go the more the time zone rules are an approximation of what was actually observed.