Game Systems/The City

City growth

The city is not a fixed backdrop. It grows where you give it access and decays where you do not, which means the network you build changes the demand it will face later.

Growth runs every 7 days.

The field#

The world is a 12,000 m square divided into a 96×96 grid of 125 m cells. Each cell carries population, jobs, land value, and a water flag. Districts are groups of cells, and district aggregates are what the demand model actually uses.

Access#

Every growth pass, each land cell computes an access score from nearby stations. A station contributes when the cell is within 1.5× that mode's walk radius, and its contribution scales with three things:

Station level — bigger stations pull harder.
Proximity — closer is better, on an inverse-distance curve.
The station's own ridership — a busy station is a stronger growth magnet than an idle one, scaled by ridership over 5,000.

That last term is the important one. Access is not just "is there a station here". A station nobody uses grows the area around it far more slowly than a station that is actually carrying people.

Growth and decay#

A cell with access above 0.5 and a meaningful population grows, at up to 3% per pass. Alongside population:

Land value rises at half the growth rate, capped at 3×.
Jobs rise at 60% of the growth rate.

A cell with no access at all decays at 0.05% per pass. It is a slow bleed, not a collapse, but an unserved area does shrink over a long game.

Between those two — access present but below 0.5 — a cell holds steady.

The feedback loop#

This is the core loop of the game:

You build a line.
It carries riders.
Ridership raises the access score around its stations.
Population, jobs and land value grow there.
More population and jobs mean more trips in the demand model.
Those trips need capacity you now have to provide.

Growth is therefore self-reinforcing but also self-complicating. A successful line generates the crowding that later degrades it — see Demand and ridership.

What this means in play#

Build where you want the city to be, not only where it is. Access drives growth, so a station placed ahead of demand can create it.
An empty station is a weak magnet. The ridership term means growth follows useful service, not track on a map.
Success creates its own problem. The corridor you grow will eventually overcrowd. Plan the capacity upgrade before the crowding penalty arrives.
Neglected areas shrink. Slowly, but over a long campaign an unserved district genuinely declines.
Land value is a lagging signal. It rises at half the population rate and caps at 3×, so it confirms a corridor is working rather than predicting it.