Migration Flow
Each day, families and single adults consider moving to your city. Applicants tend to be young adults, especially ages 20 to 34, although older people also move. Their age shapes the savings they bring.
The door in
Each vacant home gets one applicant attempt, up to the day’s intake ceiling. The household must find a lease it can afford; a failed application usually means turning back.
What sets the line. Outsiders judge your city by the last six months of published wages, job prospects, rents, safety and parks. Good news keeps attracting people after a downturn; a recovery takes time to reach them. A working household weighs the income it expects after rent against life elsewhere and the cost of moving. Some are optimistic enough to arrive without work. How many consider the city each day grows with what it offers: the jobs your employers could not fill locally and the homes standing empty travel as ads, so a town with neither hears from only one household a day, and even that one may decide against the move.
Only a share arrange a job before arriving, more often when they have a degree. They can take postings that local residents have had a week to fill. Most newcomers join the local search after arriving.
The lease screen. A household qualifies with after-tax monthly income of at least 3× the rent, or six months of rent in savings. Both spouses count, but only actual offers, pensions and basic income qualify as income. Hoping to find work is not proof of earnings. Two adults need two separate offers to count two salaries.
A small share of applicants who fail the lease screen still come. They take free shelter beds when available; only rarely do they arrive without housing. Shelters therefore help newcomers as well as residents who lose their homes. Children enrol where school seats are available, and a promised job starts only if its commute works. A family can arrive before a classroom is available.
The door out
Once a month, each household weighs a move. Some leave for ordinary reasons even when life here is going well. The strongest problem it faced that month adds pressure: prolonged joblessness, unaffordable rent, crime, no electricity, missing school places, unmet maternity care, a long hospital wait, taxes or unaffordable driving fees. A move is recorded under that problem only when its pressure, not ordinary life, tipped the household.
Young adults, renters and degree holders move more often. Children in school and older age make a household less mobile. Every income class can leave, but an ordinary move needs $1,000 in household cash. A household that cannot pay stays, even when its problems are severe.
Newcomers with no working adult may return home after three months, during their first two years. That trip needs only a $100 return fare. Households formed by residents already living here do not count as newcomers. Most households stay each month; complaints do not cause an immediate departure.
A departing employee leaves a job posting for a replacement. The census records the household’s strongest reason, its income class and whether each departing person was employed.
If a family falls two months behind on rent, they lose their home but stay in your city, waiting for an affordable home or a place in a shelter. Without a home, citizens are more likely to get sick and face an employment barrier. The barrier is drawn once per jobless spell, so more vacancies or another day do not reroll it. Moving into a home or shelter removes it. You can help them recover by providing shelters and homes they can afford. Keep that in mind before you bulldoze an occupied building: its residents will need somewhere to go, just as they would after a fire.
Flowing through
This push and pull is the spine of Everett Lee’s A Theory of Migration, a 1966 paper that still shapes how demographers think about who moves and why.
Your city is the destination, the wider world the origin, and your city’s economic, social, political and environmental conditions are the obstacles between.
| Pushes people away | Draws them in | |
|---|---|---|
| Economic | No work in your trade | Open jobs to fill |
| Social | No classroom for the kids | Good education system |
| Political | Crime | Safe streets |
| Environmental | Treeless concrete | Good parks |
Player levers
- Improve the news. Jobs, pay, affordable housing, safety and parks shape the city’s reputation over several months.
- Build workplaces people can reach. Some newcomers have an offer, while others compete with local seekers.
- Build schools before families arrive. Families may move in before places are available, leaving children waiting for enrolment.
- Keep somewhere cheaper to land. Vacancy is the release valve: with nothing open to downsize into, a priced-out household has more reason to leave instead of moving across town.
Parameters
Family ratio
0.08
Probability that an immigrant arrives with family (spouse plus 0-2 children).
Bachelors degree ratio
0.48
Share of arrivals who show up with a bachelor’s degree or higher. Whether they actually work as professionals depends on the workplaces you build; otherwise they move in and take lower work.
High school ratio
0.72
Among immigrants without a bachelor’s degree, the ratio who have at least a high school diploma.
Movers by age
The ages of the adults who move in. Most are in their twenties and early thirties, so a growing city soon needs schools, and one that stops growing slowly grows old.
| Key | Value (thousands) |
|---|---|
| Age 18 to 19 | 339 |
| Age 20 to 24 | 1855 |
| Age 25 to 29 | 1870 |
| Age 30 to 34 | 1236 |
| Age 35 to 39 | 877 |
| Age 40 to 44 | 535 |
| Age 45 to 49 | 534 |
| Age 50 to 54 | 491 |
| Age 55 to 59 | 493 |
| Age 60 to 64 | 474 |
| Age 65 to 74 | 518 |
| Age 75 plus | 329 |
Basis: measured
Source: U.S. Census Bureau, Geographic Mobility: 2023 (CPS), table 1
Min immigration cap
1
Minimum households considered per day even when the city has poor news. They may still prefer the outside option or fail the lease screen; this guarantees attempts, not arrivals.
Source: Everett S. Lee, A Theory of Migration (Demography, 1966)
Immigrant commute quarantine days
30
How long a posting stops pulling immigrants after an arrival who claimed it turned out to be unable to commute there. Only the door is closed: locals still see and can take the posting through employmentSearch.
⚠️ Source pending