Two countries, 5.4km apart
We once went looking for the city with the most distant neighbour. The other end of that list is countable too. The 524 cities in our dictionary make 137,026 possible pairs, and the shortest of them is 5.4km. An hour on foot.
| The two cities | Distance | Countries |
|---|---|---|
| Foz do Iguaçu – Puerto Iguazú | 5.4km | Brazil – Argentina |
| Victoria Falls – Livingstone | 9.2km | Zimbabwe – Zambia |
| Nice – Monaco | 13.4km | France – Monaco |
| Singapore – Johor Bahru | 14.4km | Singapore – Malaysia |
| Interlaken – Grindelwald | 14.9km | Switzerland |
| Yokohama – Kamakura | 16.1km | Japan |
| Rotterdam – The Hague | 20.3km | Netherlands |
| Gyeongju – Pohang | 21.0km | South Korea |
| Thimphu – Paro | 22.8km | Bhutan |
| Lisbon – Sintra | 22.8km | Portugal |
Three of the four closest pairs are in different countries. The Iguazu River runs between the two Iguazu towns with a single bridge over it; the Zambezi runs between Victoria Falls and Livingstone, and the Johor Strait between Singapore and Johor Bahru. All of them are closer together than Seoul and Incheon, which are 27km apart.
Nineteen pairs sit within 30km of each other, 37 within 50km, 132 within 100km. We filled the dictionary country by country, and the tightest pairs came out ignoring those compartments entirely.
From Seoul the gap is 5km
Seoul to Foz do Iguaçu is 18,671km. Seoul to Puerto Iguazú is 18,676km. The difference is 5km, which is 0.03%. On a journey to the far side of the planet the two towns are effectively the same coordinate.
They are still different countries. The flag on the journey screen changes, and the count of countries visited goes up by one. A difference that disappears on the map survives in the list.
You cross a border and the clock stays put
Measure the time difference across those close border pairs and it is zero every time. Brazil and Argentina, Zimbabwe and Zambia, Singapore and Malaysia, Denmark and Sweden — you can walk across and never touch your watch.
Other pairs break the other way.
| The two cities | Distance | Time difference |
|---|---|---|
| Amritsar – Lahore | 50.2km | 30 minutes |
| Tangier – Gibraltar | 58.1km | 1 hour |
| Lhasa – Thimphu | 284.8km | 2 hours |
Fifty kilometres for half an hour, 58km for a full hour. Time zones are drawn by countries rather than by longitude, which is how gaps like these happen. Cross from Tangier to Gibraltar and the hour changes along with the continent.
An itinerary will take both
The service picks waypoints from cities that lie along the way from origin to destination. Build the 19,432km journey from Seoul to Buenos Aires and Foz do Iguaçu and Puerto Iguazú both score a detour ratio of 1.016. Both make the shortlist, and sometimes both get drawn.
That produces a 5.4km leg. The service adds a travel day per leg and one to three nights per waypoint, so the screen ends up showing a day spent covering 5.4km. The great circle for that leg is still cut into at least 24 pieces, which puts its points 226m apart — the same code that draws a line halfway around the world.
On the map it is one dot
Zoom out and the two dots merge. At world scale 5.4km is less than a pixel. A border only appears once you have zoomed far enough in, and usually the first hint that one is there is that the place has two names.
This ranking is based on our 524 cities. Far more towns than these face each other across borders, and some of them sit closer together still. A city that is not in the dictionary does not enter the calculation.