Map creation · Part 2 · About 10 minutes
Land and water
The coastline is not drawn. It is where a sea level cuts through a height field — and the level is solved backwards from the water percentage you asked for. Understanding that one inversion explains most of what the land and water controls actually do.
The one-minute explanation
Nothing on this screen paints a country. The generator builds a height field across the whole frame, then decides where the sea sits inside it, and the land is whatever stands above that line.
The order matters, because each step only sees the result of the one before it:
A height field
Layered noise, shaped by a continental shelf whose strength and centre come from your terrain type and area, and stretched by land elongation.
A sea level, solved
The generator sorts every height in the frame and cuts at the point that makes exactly your requested fraction of it water. The percentage is a target it hits, not one it approximates.
The coast, cleaned and roughened
Cells near the waterline are smoothed repeatedly, then given back seed-stable bays and headlands at a scale that reads as geography rather than noise.
Islands added, then culled
Offshore islands are seeded into shallow water, and islands under a size threshold are sunk. Both steps follow your island density.
Only after all of that is your territory decided — and, as Part 1 noted, that is a separate question from where the land is.
Water coverage is a target, not a wish
This is the most useful thing to know about the whole screen. The sea level is not a constant that happens to produce some amount of water; it is chosen so the water comes out at your number. Ask for 35% water and 35% of the generated frame is water.
Two qualifications keep that from being the whole story.
The frame is not your country. The percentage describes the entire generated image, which includes ocean margin and any foreign territory. The share of your land that borders navigable water is a separate outcome, decided by where your border lands.
Your terrain type sets the legal band. Each profile permits a different range, and the ranges barely overlap:
| Terrain type | Water coverage | What that produces |
|---|---|---|
| Inland | 10–30% | Water is rivers and lakes. No sea access at all — the coast, where one exists, is foreign. |
| Coastal | 20–60% | A mainland with sea frontage. At the top of the range the land itself begins to fragment. |
| Island | 40–80% | Land as one or several islands inside an ocean frame, with no land neighbours. |
Because the bands overlap only at their edges, terrain type is the decision and water coverage is the adjustment inside it — not two independent sliders.
Terrain type is a shelf, and it moves with area
Coastal, Island and Inland are not three presets over the same world. Each sets how strongly a continental shelf — a broad rise centred somewhere in the frame — dominates the noise. A strong shelf makes a single compact body of land with a definite edge; a weak one lets the noise itself decide, producing something more scattered and more continental in feel.
The part that surprises people is that this value is derived from your terrain type and your total area together. A large country pulls the shelf weaker; a small one pushes it stronger. So the same Coastal setting produces a tight, obviously coastal country at 100,000 km² and something much more continental at 2,000,000 km² — the setting did not change, the interpretation did.
Land elongation
Elongation stretches the shelf along a seed-chosen axis, up to about three and a half times. It is a shape control, not a size control: the land budget is still set by water coverage, so an elongated country is the same amount of land arranged as a long corridor rather than a compact blob.
That difference is entirely a transport difference. A long country has a natural trunk axis and expensive lateral connections; a compact one has no obvious spine and many competing short routes. If you want the map to suggest a main line, raise elongation.
Island density does two opposite jobs
The control reads as a single dial but drives two separate passes:
- Spawning. Islands are seeded into shallow water away from existing land — roughly eight attempts at Few, twenty at Moderate, forty-five at Many. Deep water and cells near the coast are skipped, so the count is attempts, not guarantees.
- Culling. Everything below a size threshold is sunk again. None removes every island; Few keeps only sizeable ones; Moderate keeps much smaller ones; Many culls nothing at all.
So Few does not mean a few were added. It means several were added and the small ones were then removed. This is why lowering island density can change the mainland's own fringe, not just the open sea.
On an Island terrain type there is a further structural pass that arranges the result as a deliberate archipelago — a main island plus a few secondaries, or a single island if density is None — while keeping the land budget your water setting implies.
Which land ends up yours
Generation produces land. A second stage decides who owns it, and the rules are worth knowing because they are where a promising-looking map turns out smaller than it appeared.
- The mainland
- Your nation is grown from the largest connected landmass, starting at the cell nearest its centre. With no neighbours, all land on the map is yours. With neighbours, you keep roughly the inner three-quarters of the mainland's reach and they take the periphery.
- Islands
- An island lying completely inside the image becomes yours. One that runs off the edge stays foreign — which is why the generator pads the frame with ocean until your land sits well clear of the border.
- One connected country
- Your territory is forced to be a single piece. A pocket of your land cut off from the main body is given to a neighbour, and conversely a foreign pocket entirely surrounded by you is absorbed into your nation.
The practical reading: your usable country is smaller than the landmass you see, and the gap widens with neighbours and with the Inland profile. If a generated map looks the right size, check the territory rather than the coastline.
What water costs you afterwards
Every water cell between two places you want to connect is a decision you will pay for repeatedly.
A crossing is priced separately from the road or railway itself, as a bridge or a tunnel, and a single span longer than 55 km cannot be built at all — the confirm button stays disabled until you re-route.
A scheduled route needs both endpoints near navigable water and a genuine water path between them. The same geography that taxes your roads is what makes ports viable.
Two consequences for how you choose water coverage:
- High water on a Coastal map fragments the land, which usually means more crossings on your trunk routes, not merely a prettier coast. Water is charged at construction time and again in every kilometre of detour.
- Water is not automatically an asset. Short hops rarely beat a road once port handling time is counted, and inland lakes may sit where nobody needs to travel. Water pays when it is in the way of a corridor you would otherwise build long and expensive. Waterways: ports, routes and ferries covers what a route actually needs.
Choosing these settings deliberately
Working backwards from the country you want:
Coastal, water near the bottom of its band, elongation low to moderate, islands None or Few. You get a compact body with a coast to use rather than a coast to cross.
Coastal, elongation high. The land itself argues for one main corridor and makes lateral links expensive — a clean setting for a rail spine.
Island, water in the middle of its band, islands Moderate or Many. Water transport and aviation become structural rather than optional, since roads cannot do the work.
Inland. No ports, no ferries, no coastal shortcut — everything moves by road, rail and air, and your border is pushed away from the sea deliberately.
And one habit worth keeping from Part 1: change one of these at a time. Water coverage, elongation and island density all alter the outline, and moving all three at once tells you nothing about which produced the map in front of you.
Common misconceptions
“I asked for 30% water and my country is not 30% water”
The target applies to the whole generated frame, including ocean margin and foreign land. Your own territory's water share is a downstream result.
“Island density Few means a few islands were added”
Several are added and the small ones are then removed. The setting drives both the spawning and the culling, which is why it also changes the mainland's fringe.
“Terrain type is just a water preset”
It sets the continental shelf the land is formed from, and that value shifts with your total area. It also decides whether you may have islands or neighbours at all — and, for Inland, actively pushes your border away from the sea.
“More water means more water transport”
It means more crossings to pay for. Water transport needs endpoints near navigable water with a real path between them, and it competes with roads on total journey time including port handling.
Continue the collection
Next: relief. Why mountainousness and maximum elevation are different controls, how a height difference becomes a cost multiplier of up to five, and how rivers and vegetation are decided.