A country guessing game: name the country from its outline in six guesses.
Borderline is a free country guessing game: guess the country by its shape. Each day the silhouette of one country appears on the board, and you have six guesses to name it. After each wrong guess you are told how far your country is from the answer, which compass direction to head and how close you are as a percentage, so even a wild first guess narrows the map. Everyone gets the same country each day, and Unlimited mode serves a random country whenever you want another, without touching your daily streak.
The shape on the board is long and narrow, running from top to bottom, with a smooth coastline down its right-hand side and a ragged inland edge that hooks around something on its upper left. Without a sense of scale it could be anywhere, so you open with a probe in the middle of a continent, Chad. The clue comes back as 4,062 km away, head south-east, 79% close. South-east of Chad and about 4,000 km off means southern or eastern Africa.
A long eastern coastline in that part of the world suggests the Indian Ocean. You try Kenya. Now it says 1,988 km away, head south, 90%. Directly south of Kenya, past Tanzania, the coast belongs to a long, thin country whose border wraps around Malawi in exactly that hook. Third guess, Mozambique, solved. Two wrong guesses, and each one did a lot of work.
Distance is the great-circle distance between the centre of your guess and the centre of the answer, measured over the curve of the Earth. Neighbouring countries can still be hundreds of kilometres apart, because it is measured from centre to centre, not border to border. France and Germany, which share a long border, are 762 km apart by this measure.
The arrow is the compass heading from your country towards the answer, as you would read it on an ordinary world map, to the nearest of eight points. Closeness runs from 0% for a country on the exact opposite side of the planet to 100% for the answer itself, falling evenly with distance. The arrow tells you which way to go, and closeness tells you how far. Using both together is the whole skill of the game.
A first guess is a probe, not a shot at the answer. Unless you recognise the shape outright, pick a large, central country whose distance and direction will tell you the most. Countries in the middle of a landmass, such as Chad, Kazakhstan or Brazil, are good probes, because from there the arrow can point almost anywhere.
Then read the shape again with the clue in mind. Once you know you are looking in Southeast Asia, a long S-shaped silhouette is Vietnam, while a shape split in two by the sea is Malaysia. Lean on coastlines. Borders drawn along rivers wiggle, borders drawn by treaty run straight, and islands give a shape away almost at once.
Country shapes come from Natural Earth, a public-domain map dataset used by cartographers and newsrooms. Far-flung overseas territories are left off the outline, so French Guiana is not drawn with France and Hawaii is not drawn with the United States. The shape you see is the one you would recognise on a map. Nearby islands such as Corsica, Crete, Sicily or Tasmania are kept, because they belong to the shape.
There are 198 countries and territories that can be the daily answer, from the large and obvious to places such as Puerto Rico, Greenland, Jersey and Hong Kong. You can guess any of 238, so even a guess that cannot be the answer still returns a useful clue. The daily works through all 198 in a shuffled order before any of them comes round again.