Sister cities: how cooperative play works between two mayors

Why two, not twenty

Most online city builders bolt on a guild system and call it social. We tried to design something smaller first. A sister city is a partnership between exactly two mayors. It is the unit at which a conversation can actually happen, at which one absent player is noticeable, and at which the game can hand out meaningful shared goals without one person carrying nineteen others. Larger federations were designed alongside it as a later layer that grows out of established partnerships rather than replacing them.

This article explains the system as it works today: who can pair, how matching works, what a partnership gives you, how the weekly goal and caretaking function, and what happens when a partner stops logging in.

Who can pair, and how many partners

Partnerships are between accounts, not individual cities, with your most recently played city shown as the representative on your partner's screen. You unlock the system when a city reaches the Small City rank at 500 population and you have set a nickname. The threshold is deliberate: it is the point at which a first district is working and a new track is welcome, it keeps brand-new accounts and throwaway accounts out of the matching pool, and it means a partner has already demonstrated a few days of play.

Everyone starts with one partnership slot, and the monthly membership adds a second. Dormant partnerships, described below, do not occupy a slot.

How matching works

You can send a request directly to a mayor you have met through visiting or chat, or ask the game for recommendations. Recommendations are scored out of 100 from five signals, and the top three candidates are shown with a short greeting field so that a request is more than a button press.

Candidate cards show honest activity data such as how many of the last seven days the player logged in, because the single biggest predictor of a partnership working is that both people keep showing up. You can have at most three outgoing requests pending at once, requests expire after seven days, a dissolved pair has a three-day cooldown before re-pairing, and accounts that appear to share a device cannot pair with each other, which closes the obvious self-partnering exploit.

What a partnership gives you

• Shared tourism demand. Both cities receive +15 percent visitor demand, rising to +18 percent at bond level 3 and +20 percent at level 5. Buses and trains from your partner's city arrive carrying visitors labeled with its name. This bonus is only active while both partners have logged in within the last seven days.
• Gift bonus. Gifts of money or resources between active partners receive a 10 percent bonus on claim, 12 percent at bond level 4, capped at 50,000 money or 200 tons per gift and applied at most four times per pair in 24 hours, so two accounts cannot ping-pong value indefinitely. Partners can also send gifts from the partnership panel directly, within daily sending limits.
• Presence on the map. A low-detail silhouette of your partner's skyline appears at the edge of your map alongside a road sign, built from a tiny summary of their building positions that refreshes when they save. It is a single instanced mesh, so it costs almost nothing to render.
• Bond level. The partnership earns bond experience from play: 5 for a day on which both partners log in, 5 per qualifying gift up to three a day, 10 for caretaking, and 60 for a completed weekly goal. Levels 2 through 5 arrive at 150, 400, 800, and 1,500 experience, and each level unlocks the stronger versions of the bonuses above.

The weekly goal

Each partnership gets one cooperative goal per week, starting Monday. The first goal type is combined visitors: the sum of both cities' tourist arrivals over the week, which the game already records in daily snapshots, so no new reporting is needed from the client. The target is personalized at 70 percent of the pair's expected weekly arrivals based on the previous two weeks, with a minimum derived from city size for new tourism cities. That handicap means a pair of small cities can complete the goal just as reliably as a pair of large ones; the goal rewards consistency, not scale.

When the target is met, each partner claims a reward separately. It is delivered as a system gift of money sized to the city: 10,000 plus five per resident, up to a cap of 50,000. Pairs with no tourism history yet get a minimum goal of 100 visitors so the first week is achievable. Because the reward arrives through the normal gift claim path, it is validated by the server like any other transfer.

Caretaking an absent partner's city

If your partner has not logged in for more than 24 hours, you can look after their city once per day. The server estimates their city's tax for four hours, or six hours from bond level 3, and pays 80 percent of it to your partner and 20 percent to you, with a floor of 200 for cities that earn nothing yet and a ceiling of 100,000. Your partner sees a log entry saying who looked after their city, and if they have been away long enough to receive a re-engagement email, the email mentions it. The estimate is server-side and based on population, so there is nothing to manipulate from the client, and the mechanic exists to make an absence feel like a partner covering for you rather than a dead weight on your slot.

Dormancy and dissolution

Partnerships are honest about absence. When one partner has been away for seven days, the bonuses pause but the partnership stays active. At fourteen days it becomes dormant: the remaining partner's slot is freed and they are offered new recommendations, while the partnership itself is preserved. If the absent partner returns and both have an open slot, one click revives it with its bond level intact. Either partner can also dissolve the partnership manually, after which the same pair cannot re-form for three days. A single scheduled job handles these transitions, and in no case does a partner's absence ever apply a penalty to you; the worst that happens is that a bonus stops.

Getting the most out of it

1. Pair with someone whose log-in rhythm matches yours. Activity is weighted highest in matching for a reason.
2. If you both build tourism, the demand bonus compounds with the weekly goal. If only one of you does, the goal still works, but the bonus is one-sided.
3. Send a gift when your partner is stuck on a utility upgrade. The bonus makes a timely gift worth more than its face value.
4. Caretake when you see the option. It costs you nothing and keeps the partnership feeling alive during a gap.
5. Do not dissolve a partnership because of a week-long absence. Let dormancy handle it; revival keeps your bond level.

Tourism is the system partnerships are built around, so if you have not opened that part of the game yet, the tourism article is the place to start.