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	Maps → 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. ✅

Now drop the same bridge into a channel running east→west:

Its west and east ends land in the water. ❌
Its middle sits on dry land. ❌

Both ends fail at once, so the site is refused. The generator also never looks there in the first place — it scans for runs of water crossing the bridge's own axis, so a channel running the same way produces no candidates at all.

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.