PeterTheDataScientist/gridtruth

Which African cities go dark, and how often. Every city measured against its own night-time brightness baseline from VIIRS satellite data. Open data, no account needed. # GridTruth **Which African cities go dark, and how often. Measured from orbit, so no utility has to agree to be measured.** **Open the dashboard** --- There is no open, comparable record of electricity reliability across Africa. Utilities publish little, publish inconsistently, or publish nothing. Zimbabwe's ZETDC answers the question "Why is ZETDC not sticking to the schedules it advertised?" by stating that load "will be done outside the programme without notice", and then publishes no programme at all. So this stops asking. The VIIRS Day-Night Band has photographed every square kilometre of Africa every night since January 2012, at 500 m. One instrument, one calibration, no permission required. ## What it measures, and what it refuses to measure **Every city is compared to its own history. Never to another city.** That distinction is the entire project. A map coloured by absolute brightness is a map of population density and wealth: it would look authoritative and mean nothing. What this asks instead is *is this place darker than it normally is*, which is answerable for Harare and Lagos and a small town alike, because each is only ever compared to itself. The measurement unit is the city's **own lit footprint**, not a box drawn around its centre. Each pixel's normal level is the 90th percentile of that pixel across all observations; pixels that never light up are excluded. The headline number, `dark_share`, is the fraction of that footprint sitting below half its own normal on a given night. Using a box instead of a footprint is not a small error. It made Cape Town read five times dimmer than Johannesburg, because a quarter of Cape Town's box is ocean. That is written up in FAILURES.md. ## Status: preview, not a finding 26 cities, sampled at every new moon from 2022 onward, collection ongoing. Lunar brightening is controlled by sampling near new moon and recording the phase on every observation. Poor-coverage nights are discarded. **Thin cloud is …