Docks, piers and bridges — structures that need something other than a field.
Water & Crossings
Most structures stand on a patch of dry ground. A few do not: a dock reaches into a lake, a pier sits on the boundary, a bridge crosses a river and touches land only at its ends.
Two settings cover all of it. Ground it needs says what has to be under the footprint; a crossing rule says what has to be under each part of it.
Where to Author It
| What | Where |
|---|---|
| What ground a prefab needs | Zones → right-click the map → Structure Prefab… → Placement → Ground it needs |
| Whether it crosses something | Same dialog, Crossing tab |
Ground It Needs
| Value | Every tile under it must be | Use it for |
|---|---|---|
| Dry land | walkable ground | everything ordinary — this is the default |
| Water | water | moored ships, buoys, lily rafts, a lighthouse rock |
| The water's edge | the footprint must touch both | piers, boathouses, slipways, watermills |
| Anything | just be on the map | rubble and debris, which suit broken ground |
Each one is searched for differently, which matters more than it sounds. A dock is not found by checking whether random spots happen to be wet — the generator walks the actual coastline looking for it. Without that, a lake covering three per cent of a map would get a dock about three per cent as often as it should.
Cliffs are refused by every value except "Anything". A cliff is a hole in the map rather than a surface, and a stamp cannot regrade the land under itself, so a building placed across one ends up half-buried.
Crossing Rules
A bridge is not one patch of ground, it is three: a bank, the water, and the far bank. The Crossing tab splits the footprint into three bands along the direction it runs and lets each say what it needs.
For a bridge that is land · water · land. That single line is the whole rule, and it is also what stops the bridge appearing in the wrong place.
| Field | What it does |
|---|---|
| Direction it runs | West→east or north→south. The direction the traffic goes, which is the long axis of the map you drew. |
| Near end / far end — tiles | How much of the footprint is abutment at each end. Two or three tiles is usual. |
| Each band must be | The ground that band needs, using the same four values as above. |
The bands are strict at the ends and forgiving in the middle: both abutments must be entirely what they asked for, because one water tile under an abutment is a bridge ending in a river. The middle only has to contain what it crosses, because a real channel is never exactly as wide as the span — demanding an exact match would mean a bridge only ever fits rivers of one precise width.
Why a Bridge Never Lands in the Wrong Gap
This is the point of the whole feature. Take a bridge drawn running west→east and a channel running north→south:
- Its west and east ends land on the two banks. ✅
- Its middle sits over the water. ✅
- Its west and east ends land in the water. ❌
- Its middle sits on dry land. ❌
Two Orientations Means Two Maps
A stamped prefab cannot be rotated. Isometric art is directional: wall facades, roof rows, door sprites and autotile edges are all drawn facing one way, and a turned copy renders as mismatched edges. There is no setting that fixes this.
So a bridge that should appear in both directions is two maps — one drawn west→east, one drawn north→south — linked in a variant group so they behave as one thing. See Structure Relations.
Gotchas
> A bridge with no crossing rule is a building. It will place happily in the middle of a field. Choosing the bridge kind fills in a starting rule for you; if you clear it, nothing will stop it.
> The ends must leave a middle. Two ends of 3 tiles on a 6-tile span leave nothing to cross, so the crossing requirement stops meaning anything. The editor refuses to save it, and if a map is later shrunk until the rule no longer fits, the prefab is withheld from generation entirely and named in the log — rather than quietly reverting to a building standing on grass.
> Wider than it can reach is not a crossing. A ten-tile bridge with 2-tile ends spans six tiles of water. A twenty-tile river is not a site for it, and no amount of density will make it one. Draw a longer bridge.
> Listing a water biome does nothing on its own. Biomes decide which prefabs are eligible; the ground rule decides what they can stand on. A cottage listed for ocean still needs dry land.
> Studio or Enterprise tier, like the rest of map generation.