Readings from a neighbourhood add up into a city score, and cities into their region. That is as far as the adding goes.
This is the detailed companion to the Index: how a score gets built, level by level. A neighbourhood sits inside its city, the city inside its region. Each level gets the same score, worked out the same way. Above the region sit two wider views the Index watches but does not add into: the natural region a city sits in, and the planet. They are the limits a score has to stay inside.
Aggregation levels
Why the adding stops at the region. The framework gives three of the five levels a job of adding up (neighbourhood, city, region) and the top two a job of setting limits. The neighbourhood is where the sensors touch the ground; the city is the first level of government that can act; the region is the last. Above the region sit the bioregion's carrying capacity and the planet's broken limits. These are watched, not built up from below.
This matters because people ask why there is no single bioregion score the way there is for a region. No government sits at the bioregion or the planet that could take such a score and act on it fast enough to matter, and that speed is ρ. There is only ecological and planetary reference. The levels make that gap plain to see.
↪ Next: read the scale-by-scale walk (these levels told as a story), or open the aggregation rules for the method behind each step up. New: see the same levels drawn on real maps in the aggregation map.