Settlements, transport service and metros

The one-minute explanation

Every settlement carries three service facts, printed in its detail panel:

These are the levers through which infrastructure reaches everything else: GDP, government grants, population tax, development growth and decay, and migration. A settlement with impressive infrastructure but poor completed movement is, to the economy, poorly served.

The transport service score

The score is a product of two factors, each a percentage:

Coverage asks how much service is available; service quality asks how well that service is operating—delivered service divided by installed service. Because the two multiply, a dense network with badly running services scores no better than a sparse one. The national figure is the population-weighted average, so improvements in large settlements move it more.

Coverage counts what is connected. Each road link contributes points by grade—an expressway is worth several local roads—and both endpoints benefit. Railways contribute only where a published operating line actually stops: track without service, or a station a line merely passes through, adds nothing. Active air routes and water routes add fixed contributions per route.

Coverage has diminishing returns: the first strong connections transform the score, while the tenth adds little. A settlement cannot reach a high score by accumulating local tracks alone, and it cannot exceed the scale of what useful grades provide.

Quality is judged differently per mode: a road by its average speed against its limit, a railway by its busiest-direction load against capacity, an air service by its peak directional load factor—best in a balanced band of roughly 62–88%, penalized both when nearly empty and when overfull—and a water route simply by whether it is running. Road and rail discounts reach at most half the affected contribution; a suspended water route contributes nothing at all. The same congestion also acts on the settlement directly, as described below.

As a reading aid, scores below 25 mean very limited service, 25–49 weak, 50–74 moderate, 75–89 strong, and 90 or above excellent. Accessibility rates read on a coarser scale: below 40% is low, 40–79% medium, 80% and above high.

Accessibility: completed versus desired travel

Accessibility comes from the demand model, not from the map. For each settlement it compares, per axis, the movement actually carried with the movement the settlement’s demand relationships wanted—after routing, capacity and suppression have taken their toll. Passenger and cargo accessibility are deliberately independent: a freight corridor does not make hospitals reachable.

A dash in the panel means no measured demand exists for that axis yet, which is neutral—not a zero. A displayed 0% is real and means wanted trips are not happening.

Accessibility is what connects this article to Travel demand, traffic and capacity: everything that suppresses or strands demand—slow paths, heavy charges, missing connections, full capacity—reappears here as a lower accessibility rate.

What the three measures feed

GDP

The service score multiplies each settlement’s economic output, up to ×1.8 at a perfect score. The curve is steep at the start: the first useful connections have the largest marginal effect.

Public revenue

Grants pay a protected floor plus an earned share scaled by the population-weighted national service score, and both grants and the population tax are further scaled by national and local passenger accessibility. See Where public money comes from.

Development growth

Cargo accessibility gates the goods-producing fields, passenger accessibility gates the people-serving fields, and busy hubs and corridors add commerce and logistics growth on top.

Development maintenance

Two decay channels: a mature settlement erodes when its service score stays far below what its development level requires, and separately when its residents complete too few of their desired trips. Early-stage settlements are protected from both.

Migration

Both the service score and passenger accessibility act as pulls measured against the national average—people move toward relatively better-served places.

Policies

A boomtown policy delivers only 30% of its designed surge to an unconnected settlement, scaling up to full strength with the service score.

Congestion strikes twice

Road congestion at a settlement acts through two separate channels.

First, it lowers the service score itself, which weakens everything above. Second, sustained saturation applies a direct penalty: the settlement’s worst congested link sets a strength (moderate for saturated, strong for over-saturated), which each month erodes human capital, technology, logistics, commerce and tourism—and pushes residents out on top. Most of those residents resettle inside the same commute shed, so a congested core feeds its own suburbs. Unlike the service decay channels, this erosion has no protective floor worth relying on.

Only roads congest this way. Overbooked railways do not degrade the city; their excess demand simply spills to other modes or goes unserved.

Reading service on the map

The service overlay adds a coloured dot beside each settlement label, on a continuous ramp from red (0) through yellow (around 50) to green (100), with the exact score in the tooltip. It is the fastest way to spot the pattern this article describes: a chain of green along a well-run corridor, and the red pocket where a region’s demand is not being completed.

Metro clusters

Settlements near a larger neighbour merge into a metro for the City Map. Each settlement projects an influence radius that grows with population—roughly a nine-kilometre radius at one million people, twenty-five at ten million. A settlement inside a larger neighbour’s radius is absorbed; two settlements of at least 50,000 whose radii overlap merge as equals. Below 50,000 a place can be absorbed but never anchors a metro.

The metro takes the name of its largest member, and Enter City Map on any member opens the shared metro map. Membership is recomputed quarterly as populations change, so metros grow, merge and annex suburbs over time.

A metro is a City-Map grouping, and it is also the anchor of a commute shed. Service, accessibility and taxes remain per settlement, but migration does not: a settlement that can reach a metropolitan core within 60 minutes of ground travel shares that core's jobs and income, because its residents can work there. A core is the national capital, a provincial capital, or a metro of at least 200,000 residents. Weight falls off with travel time, so halving a journey is worth far more than adding another connection elsewhere—and only roads, rail lines an operating service actually runs, and passenger-carrying water routes count. Flights are never commuting. What a metro additionally carries is its City Map—and the completeness feedback and landmark ranking that come with it, described in Designing your cities.

How to read a struggling settlement

1. Open the panel’s three service facts. Low operational quality points to coverage or congestion; low accessibility with good quality points to demand-side problems—suppression, capacity, missing partners.
2. Distinguish the two decay channels. Service-score decay responds to building and decongesting; accessibility decay responds to completing trips, which may need pricing or capacity changes rather than new links.
3. Check the population breakdown. The growth row itemizes the migration components, including transport efficiency and passenger accessibility versus the nation.
4. Look for the congestion penalty. One over-saturated link is enough to set the settlement’s full penalty; relieving the single worst link removes it.
5. Remember comparisons are national. Migration pulls are relative—improving everywhere equally moves no one.

Common misconceptions

“Building a railway raised my service score”

Only operating lines that stop at the settlement count. Track, and stations that services pass through, contribute nothing until a line serves them.

“Service is one number”

Operational quality, passenger accessibility and cargo accessibility move independently and feed different parts of the economy. A freight-only hub can have excellent cargo accessibility and poor passenger accessibility—and its tourism, healthcare and education will show it.

“A metro is only a City-Map grouping”

Taxes, service and development remain per settlement, and a metro’s population total still governs its city’s footprint and landmark ranking. Migration is the exception: a core’s jobs and income reach everything inside its 60-minute commute shed, and residents a congested core pushes out mostly resettle inside that same shed rather than scattering across the country.

Related reading

• Travel demand, traffic and capacity — where accessibility comes from.
• GDP, population and development — the fundamentals these measures feed.
• Designing your cities — what a metro’s city map does.