Five lines that loop back on themselves

A subway line that circles back to its start sounds simple. In practice, the five loop lines in the game are all different, and each has caused a decision in our data about where a typed run should begin and end.

A true ring: Yamanote and Seoul Line 2

The Yamanote Line in Tokyo is a clean ring of thirty stations. It began service between Shinagawa and Akabane in 1909, and it only became a full loop in 1925, when the viaduct between Ueno and Tokyo opened. Seoul Line 2 is the other true ring, forty-three stations, with its first stretch opening on October 31, 1980 and the loop closed on May 22, 1984. In the game both have a closing segment on the map that does not repeat the first station, so you type each name once.

A spiral: London's Circle line

The Circle line was a ring until 2009. It was then extended west to Hammersmith and now leaves Hammersmith, joins the ring at Edgware Road, goes all the way round and ends at Edgware Road again. Paddington and Edgware Road are therefore stops that the train visits twice. It is less a circle than the letter Q.

A figure six: Tokyo's Oedo Line

The Oedo Line is shaped like the number 6. A straight stretch runs from Hikarigaoka to Tochomae, then the line circles through central Tokyo and comes back to Tochomae. That means Tochomae has to sit twice in the station list for the map to be drawn correctly, but we only ask you to type it once. The line has thirty-eight stations, and with about 478 keystrokes it is the hardest line in Tokyo.

A loop with a tail: Seoul Line 6

Line 6 is the oddest. Trains run from Eungam to Yeokchon and on to Gusan, then back into Eungam, then on to Saejeol and the rest of the line. The loop around Eungam is real. We wanted the run to begin at Yeokchon, but the map still has to show the stretch from Eungam to Yeokchon, so we added a separate starting point to the data. The route is drawn in full, and the typing begins at Yeokchon, goes around and passes Eungam only once.

Why we care

Each of these needed a different answer to the same question: should the player type a station twice just because the train visits it twice? We said no each time, and kept the map faithful to the tracks. If you want to see how that feels, ride the Yamanote Line first, because it is the simplest, and the Oedo Line last.