Mapping the World’s Time Zones
A world map showing only the time zones; just the borders between those zones, without any context. It creates a somewhat confusing image: straight lines that occasionally form right angles and suddenly turn into messy winding lines. But then suddenly you spot it: coastlines and national borders, Iceland, India, Argentina.
With some colors added, such a map seemed like a nice addition to my collection of world maps. But before that map was finished, I discovered some fascinating facts about international timekeeping.

Full and half hours
How many time zones are there on our planet? Twenty-four, you might think, one for each hour of the day. But there are more. Some countries are quirky and don’t use a one or two hour time difference with neighboring time zones, but rather a half hour. For example, India, Myanmar, Iran, Afghanistan, and Venezuela. Also, in Canada’s Newfoundland, it’s half an hour earlier than on the two small French islands off the coast.
Nepal is even more stubborn: it’s a quarter of an hour later there than in India. And on the Chatham Islands of New Zealand (about 700 inhabitants), it’s three-quarters of an hour later than in the rest of the country. It’s as if the island of Schiermonnikoog had its own time zone…
Anyway, maybe the rest of the world is quirky. Time is an arbitrary choice. We could have just as well agreed to use Kathmandu as the reference point for the prime meridian, instead of Greenwich.

Erratic borders
In places where no one lives, the polar regions and oceans, the time zones look simple: they are defined by straight north-south lines, parallel to the meridians. But as soon as those lines touch land, they go all over the place, following borders created by humans. After all, it’s handy to have the same time across an entire country, when possible.
Some countries are so large that one time zone isn’t enough. Russia, for example, has no less than eleven time zones. The Americans have five, with strikingly irregular borders. You’d expect the often perfectly straight borders between states to work well as time zone borders, but some states have multiple time zones.
In China, they keep it simple. That country has a single time zone for all its 1.4 billion people. Greenland, on the other hand, splits its 60,000 inhabitants across no fewer than four time zones.

Time differences
The largest time difference on either side of a national border is no less than three and a half hours. But there won’t be too many people crossing that border between China and Afghanistan: the map only shows a footpath over a pass at nearly 5000 meters above sea level.
In the waters around the island nation of Kiribati, the time differences are even more dramatic. That country used to be exactly on the international date line but moved it to the east in 1995. Not only because that way they can celebrate the New Year first. But also because it’s impractical to have a date line split your country in two. The result, however, is a twenty-four-hour time difference with French Polynesia, the next archipelago to the south.

Westward
Another thing that stands out: most time zones have a tendency to spread westward. In other words, to the west of the actual zone there’s an area where it should technically be a little earlier than the clock shows. In these areas, the sunrise and sunset happen later than you would expect based on their position on the globe.
The Netherlands is a good example of this. In fact, we use the time of Prague. As a consequence the sun doesn’t reach its highest point at noon but at 12:39. Some people think we should therefore switch to Greenwich Mean Time. Although the sun would then be slightly too early in the zenith.
But globally, it’s quite common for the actual time to run ahead of solar time. For example, in all eleven Russian time zones, it gets light quite late in the morning and dark quite late in the evening.

Daylight saving time
If you include daylight saving time, that westward deviation becomes even stronger. Especially in temperate latitudes, many countries use daylight saving time. In the tropics, it doesn’t make much sense because day and night are about the same length year-round. Near the poles, it’s already light for a long time in the summer, so shifting time doesn’t make much sense either. But in the areas between, periodically adjusting the clock can make a difference.
The length of the daylight saving time period and the date on which the clock is adjusted varies. For example, in Morocco, it’s daylight saving time for eleven months of the year. Only during Ramadan does it briefly switch to winter time, so the wait for Iftar isn’t too long.
Anyway, including daylight saving time would make the map very complicated, so I left it out of my world time zone map.

Colors and shadows
Knowing all these facts, it becomes even more fun to have such a time zone map on the wall above the couch. The color scheme is based on the full 360 degrees of the color wheel. For clarity, I also added a shadow, as if each hour shifts under the next. With an extra strong shadow at the location of the date line, where the new day crawls over the old one.
I briefly considered putting the hours of difference from Greenwich on the map as well, but ultimately decided not to. As a collection of almost abstract color blocks, this world map is simply the most beautiful. For those who want more information about time zones, there’s plenty to find online, such as this interactive map.
