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Why ordinary GPS is off by metres, yet you can measure to centimetres. Base stations, carrier phase, NTRIP, Fix/Float and QZSS CLAS.

Where the error actually comes from: the ionosphere, reflections, satellite geometry. What you can fix yourself, and where the limit of a single receiver lies.

GPS is the name of one system; GNSS is the umbrella term. GLONASS, Galileo, BeiDou, QZSS, and the benefits of multi-GNSS.

Degrees-minutes-seconds, decimal degrees, plane rectangular and UTM. Why an old datum puts you 400 m away, and why the height a receiver reports is not the height on a map.

How base-station corrections reach you over the internet. Caster, mountpoint, client and the connection flow.

The standard format for raw GNSS observations. The difference from NMEA (the answer), .obs/.nav, Hatanaka compression, and use in PPK/PPP post-processing.

2,485 public RTK base stations worldwide, served as one open list. The device measures the distance itself and connects to the nearest one. Source code included, MIT.

Static, RTK and network RTK: what to choose and when. How a drone gets centimetre positions, and the step everyone skips before trusting the result.

22 GNSS logs from Tokachi compared cell by cell: 0.53 m apart horizontally, 122 m apart in height. How the cause was isolated, with the data.

Live buses, 6,962 stops with next arrivals, the Subte, safety data and 84 historical events, and how to ride the bus.

What it is actually like on the surface, read from measurements: fourteen Earth-years of readings from Gale Crater, and the night-time infrared record of the whole planet.

The distance changes every second. Computed live from orbital elements, with the light-travel time and why the number swings between 55 and 400 million kilometres.

All 24 places where a craft has come down, on measured lunar terrain. Apollo, Luna, Chang'e, Chandrayaan and the recent commercial landers.

2,048 features carry an official name, and the IAU recorded why each one was chosen. Craters under 60 km take the names of small towns on Earth, so villages from 106 countries and cultures sit on another planet.

2,023 named features and the reason each name was chosen. Most are people who studied the sky. 7,063 smaller craters share those names with a letter added, listed on the page of the name they belong to.

Elevation measured by laser, night-time infrared, the day-night line moving in real time, and 1,952 named features.

Measured lunar terrain with the landing sites marked, and the phase as it is tonight.

Sixteen layers built for Japan: bear sightings, flood and landslide risk, snow depth, lightning, tornadoes, fatal crashes, bus stops, medical reach, population density and nationwide 3D terrain.