Lay your city out on the site and your lines are checked against the map. First test: take it to 100,000 people with every line and all four stretches holding. Second: found a city from nothing and keep it whole for 20 years.
Periopolis works a city out from premises without the private car: nobody drives or parks inside it, daily needs are a walk away, and longer trips ride shared movers on a line. The same arithmetic is run for a car city of the same size, so every result can be checked against cities that exist. The claim is that such a city can be planned, built, filled and powered, and the Board shows where that claim still rests on a guess.
Every figure carries a mark. Sourced has an outside citation with its source and year. Yours is a design choice, from the numbered lines. Mine is a placeholder nobody stands behind yet: those are the gaps.
The source, the premises and every decision are at github.com/ChicagoDave/periopolis. To review it, open a review issue: say what you do, what holds, what does not, and anything the model cannot answer. Copy the city as text, under the map, puts a city you changed into your reply.
Each of these is one of the four stretch tests come true. A city that holds all four cannot be broken by any of them.
| Year | People | Broken | Opened | Spent |
|---|
| Year | Month | People | Homes for | Moved in | Born | Died | Moved away |
|---|
Line 18. The same board with the city pushed to the edge of its 20% band, or with one stretch of its mover line closed. These four are everything the clock can deal.
The day of the people living here now. Its trips add up to the day's, its busiest hour is the 10% the movers are sized for, and its highest power is the peak the reactors carry, so the day and the lines cannot disagree.
| Hour | Trips | On a mover | Movers moving | Power, MW | Pupils |
|---|
Lines 24 to 29. Every tile and stretch priced at the ledger's unit costs, in six layers, beside a car city of the same size. Every unit cost carries a mark: Yours from the lines, Sourced, accepted with its source and year, Sourced and a placeholder until accepted, or Mine until a source is found. Housing is paid for once, through Financing; who pays is a later question.
| Layer | This city | A person | Car city, a person |
|---|
| Spent by layer | So far |
|---|
| Row | How many, at what | Cost | Mark |
|---|
One tile is the ground of one center: 5,000 people in three-story townhouses on 93 acres, with a bakery, butcher, cafés, library, doctor and park in the middle. The farthest home is a 6-minute walk from it. Neighboring centers are a 10-minute walk apart.
Lines 1, 2, 7 to 9, 11 and 12 are not pieces on the board. They are built into every tile the way the ledger worked them out.
The rates are the ledger's: who makes which trips, what a school holds, what a ring building serves. The distances are this map's. So a tight layout and a stretched one score differently, and neither matches the ledger's round city exactly.
Ground taken counts every tile you build on, the ring and the plants included. The car city's figure leaves its plants out.
Ten crews, one job each. A neighborhood, a ring building, a high school or a plant unit takes two years. A smaller school, fields, a stretch of line or a further reactor module takes one. A reactor site with its first module takes three.
People move in the year their homes are finished, and a school opens with its neighborhood. Each year the city is checked as it stands, and every broken line counts one line-year against the run.
With people arriving month by month, a finished neighborhood stands empty and fills at no more than 4,800 people a year across the city, Irvine's pace between 1980 and 1990. Each month people are born, die and move away at the national rates; half of those who move house leave the city. Crews still work by the year. A neighborhood still filling is a watch on its daily list, not a break.
Five things happen in a run, each announced a year or two ahead: a housing squeeze, a wave of children that moves up a grade a year, a slump, and two closures of a stretch of line.
A cost row is one count times one unit cost. A neighborhood is one center's share of the ledger's city: its streets, floor, entries, pipe, lanes and dumbwaiters cost exactly what the ledger's column gives it. A ring building is one building's worth of the middle's floor; a plant is its modules or units; a stretch of line is a step of floor and track. Schools and fields are inside the floor and the parks, so they add nothing. The car city is the ledger's, at this city's population.
To build is paid as things finish, so a piece taken down comes off that year's spend. To run is paid every year for what stands. Year 0 spends nothing. Dollars are of each source's year, not escalated. Every premise was accepted on 2026-10-14: a sourced figure keeps its source, and the rest are yours. Water follows the green ground, so a city of lawns drinks more than a city of townhouses. The city indemnifies its citizens, so no one here carries insurance (line 29). The city also carries what a state would: welfare, higher education, administration, corrections and courts a person, and the running of its streets and parks by the square meter, so a city of streets pays more to run them.