It is called the Multiverse Passages Mapping Initiative, a consisted attempt to chart and map all known Passages and Places. Originally started by scholars at The College, it now describes dozens of disconnected pieces of information, of varying levels of trustworthiness.
Most people simply call them Maps.
People have died and killed for Maps.
As previously mentioned, even knowing where a Passage is, it is still non-trivial to find it again, let alone map it. Most of the most travelled Passages (about 80) in Thyra are signalled by a bright red circle on the ground, drawn around it, about one meter in diameter, with the Passage number written a number of times around the perimeter. If you aim for the centre of the circle, most times you go through. If not, you turn back and try again.
Some passages have black circles, and other warning signs, mostly those that have the potential to kill you in instants (toxic/no atmosphere, aggressive fauna/flora around the Passage end, aggressive populations, the list goes on)
Some passages are only rumoured or mythical, and may or may not exist. The official Maps refer to them by letter combinations (instead of numbers). Only once has a lettered passage become a numbered one (Passage BK became passage 20). The reason behind this is a simple one: if you find a Passage yourself, that has a lot of money potential, you won't necessarily share it with the world.
According to Professor Gregor Wallinsky, geographer at The College, between official, unofficial and quasi-mythical Passages (including Land, Water, Air and Below Passages), their total number to present is somewhere in the vicinity of 250.