City Distance Estimation Game

About Geo Distance

Geo Distance names two cities and asks how far apart they are in a straight line over the surface of the Earth, in kilometres. You slide to your estimate on a logarithmic scale from 100 to 20,000 km. There is no map to help you; you must use what you know about the world.

The pool has 45 cities on all continents, from Reykjavik and Oslo to Auckland and Buenos Aires. The distance is at least 250 km, and on the first levels it stays below 12,000 km. The real distance is computed from the coordinates of the cities with the great-circle formula, so it is the shortest route over the globe and not the length of a road.

How to play

1. Read the names of the two cities and place them on a mental map.
2. Think of a known distance for reference: London to Paris is about 340 km, London to New York about 5,570 km.
3. Slide to your estimate. The slider is logarithmic, so the left side has finer steps.
4. Lock in. The real distance is shown on the slider, rounded to 10 km.

Two cities are shown. Slide to the distance between them in kilometres, as the crow flies over the Earth's surface. The slider is logarithmic.

How scoring works

The score depends on the ratio between your estimate and the real distance on a logarithmic scale, so being twice too far is as wrong as being half the distance. A perfect answer gives 100 and the score reaches 0 at a factor of about 2.2 on level 1 and 1.5 on level 10. At the top level an estimate that is 20 percent off still earns about 55 points.

The distance is the great-circle distance on a sphere of radius 6,371 km, computed from the latitude and longitude of the city centres, and rounded to the nearest 10 km. The time limit is 16 seconds on level 1 and 12 seconds on level 10.

What it trains

The game trains your mental map of the world and your feel for large distances. It is useful for travel planning, for understanding news from far away and for judging the length of a flight.

It also challenges the distortions of the maps we usually see. On a flat map, distances near the poles look larger than they are, and routes over the ocean look longer.

Tips for a higher score

• Build reference distances: Amsterdam to Berlin is about 580 km, London to Moscow about 2,500 km, and New York to Los Angeles about 3,940 km.
• Use flight times. A flight of one hour covers around 800 km, so a 10-hour flight is about 8,000 km.
• The longest possible distance is about 20,000 km, halfway around the Earth, which is a useful upper limit.
• Remember that the shortest route over the globe often passes close to the poles, so it looks curved on a flat map.
• Compare with the circumference of the Earth, about 40,000 km. A quarter of that is 10,000 km.

The idea behind it

The shortest path between two points on a sphere follows a great circle, and the distance is computed with the haversine formula, which has been used in navigation since the nineteenth century. The Earth is not a perfect sphere, so the true distance can differ by up to about 0.5 percent, which is far less than the tolerance of the game.

Research on mental maps has shown that people's knowledge of geography is distorted in systematic ways. In a classic 1978 study, Albert Stevens and Patty Coupe found that many people believe that Reno is east of San Diego, when it lies to the west, because they remember California and Nevada as separate blocks with a fixed relation instead of as exact positions.

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Free, no account. Your best scores are saved on your device.