A field guide for engineers arriving from abroad. Six pages, written from primary sources and from this site's own measurements; dates on every number. Start with the satellites, end with the rules and the cost of living.
Japan runs a positioning ecosystem that is unusual in three ways, and none of the three is explained well in English. It broadcasts free centimetre-level corrections from satellites (CLAS) and a free regional PPP service (MADOCA-PPP) that reaches from Southeast Asia to Australia. It maintains about 1,300 state reference stations whose real-time data reach users only through commercial providers, while a few hundred community base stations are open to anyone. And it has its own answers for coordinates: a 2025 revision of every height in the country, and a plane coordinate system with 19 zones where X points north.
This guide is the map of that ecosystem. It does not compete with the official documentation; it tells you which official page to read, what the numbers there mean in the field, and which of this site's free tools applies. It is written by an engineer in Obihiro, Hokkaido, who measures with this equipment every week, and it will be kept current: when a satellite launches or a standard changes, the page changes and the date on it changes.