Vellum

An atelier of imaginary cartography.

Vellum lives at https://www.vellumworlds.com/. No install, no account: the whole engine runs client-side in your browser.

Vellum surveys worlds that don't exist and drafts them as atlas charts. Give it a seed and it invents a landmass, simulates the rain that carves its rivers, grows its forests, founds its harbor towns, names everything in one of ten invented languages, and partitions the land into quarrelsome realms. Then Vellum sits down at the drafting table and draws the maps, complete with parchment texture, hatched mountain ranges, a compass rose, a sea serpent, and a title cartouche.

Room	What happens there
Explorer	Type a seed, draw its world, zoom into its regions
Reading Room	Watch any seed's world unfold: the founding voyage, then its recorded ages, on one continuous timeline
Print Room	Poster-size SVG or PNG of any seed, print the bound atlas to PDF, download a self-contained atlas
Seed of the Day	Today's world, the same for everyone, plus the Daily Hunt
Atlas	The hero world (seed 42) as a bound volume
Gallery	A twelve-world contact sheet
Q & A · Glossary	How it all works; the vocabulary printed on the charts

The Atlas is drawn into the site at build time rather than authored as a page, and the Gallery's charts are generated the same way.

The daily seed is the current UTC date read as an integer YYYYMMDD, so everyone sees the same world on the same calendar day, and the page never needs a rebuild: it draws itself in your browser when you load it.

Same seed, same world

Every chart is reproducible from the number printed in its corner. The root <svg> embeds its full recipe as data-vellum-* attributes, and re-rendering that recipe reproduces the map byte for byte. The Q & A covers seeds, determinism, and how to reproduce a saved chart in detail.

The styles

• antique: parchment, waterlined coasts, hatched mountain glyphs, tree fields, realm tints, rhumb lines, cartouche, sea monsters.
• topographic: hypsometric tints, shallow-water bands, contour lines, cased red roads. A modern survey plate.
• ink: monochrome pen-and-ink linework.
• nautical: white-water sea chart with fathom soundings scattered over open water, a shoal tint out to the dashed danger line, rock-awash marks, prevailing-wind arrows, navy linework, prominent rhumb lines.

How a world gets made

Each stage is a pure function of the stage before it, and every random choice comes from a labeled fork of the master seed (fork("names"), fork("sites") …), so adding a stage never reshuffles the others.

1. Terrain: domain-warped fractal gradient noise with a ridged component, shaped by map-type falloff. Sea level is chosen by quantile so the land fraction always hits its target.
2. Hydrology: priority-flood depression filling guarantees every land cell drains to the ocean; D8 steepest descent + moisture- weighted rain accumulate into rivers with tapered widths and tributary junctions.
3. Climate & biomes: latitude + elevation lapse temperature, coast/river-distance moisture, a Whittaker-style biome matrix with alpine and shoreline overrides.
4. Society: settlements scored by harbors, river mouths, and flat fertile land; roads grown by Dijkstra with a reuse discount so trunk corridors emerge; realms partitioned by terrain-cost Voronoi, with borders that prefer ridges and rivers.
5. Names & lore: syllable-grammar generators for ten invented cultures name every town, river, sea, and realm; a template-grammar lore writer drafts the gazetteer notes.
6. Rendering: marching-squares coastlines and contours (with saddle resolution and boundary closing), Chaikin smoothing, a tiny immutable SVG builder, and ~15 layer renderers up through the parchment-texture overlay (feTurbulence) and frame.

Regional zoom falls out of the architecture: elevation is a continuous function of world-space coordinates, so the atlas's "Environs of …" charts re-sample the same world through a smaller window at finer resolution; coastlines, mountains, and settlements all line up with the world chart.

Inventing a name language

Each of the ten name cultures is a plain data object (the Culture type in src/society/names.ts): three sound inventories (onsets, nuclei, codas), the syllable patterns that combine them, and the templates that dress a bare stem into "The Sea of %" or "Mount %". Retune one, or add your own to lean a world's names toward any sound you like. It is phonotactic mimicry, not linguistics: a culture captures the shape and sound of a language, never its grammar or meaning.

One warning: names come from a labeled fork of the seed, so editing the cultures renames every world. A naming change re-rolls existing seeds, owes a hero-chart regen (npm run charts:regen + npm run og), and must respect the covenant seed: seed 42's culture pick must keep landing on oromi across roster changes, so the golden world's every name stays bit-identical. test/world/covenant-seed42.test.ts fails loudly if it ever moves. A culture's id is world identity too: a world founded from a sentence names its culture by id, so an id is never renamed.

Run it locally

git clone https://github.com/ahl-gram/Vellum
cd Vellum
npm install
npm run dev        # the full site, Explorer included, on a local Astro dev server

Vellum needs Node 24+.

The CLI

The engine is also a command-line tool that draws one chart at a time, straight from the TypeScript source with no build step:

npm run chart -- --seed 42                     # → out/chart-42-antique.svg
npm run chart -- --seed 42 --style nautical    # a different drafting table
npm run chart -- --seed 42 --theme moisture    # a thematic data plate (rainfall)
node src/cli/main.ts help                      # the full flag reference

Charts land in out/ (gitignored) as plain SVGs: open them in a browser, drop them into a document, or add --png to rasterize. The help screen documents every flag (styles, map types, climate bands, coastline raggedness, legends, coats of arms, PNG export).

Development notes

Built test-first for the algorithmic core (RNG, noise, marching squares, flow, rivers, biomes, names, placement) with structural tests pinning the renderer's contract (layer ids, balanced tags, no NaN, byte-determinism). Aesthetics were iterated with a screenshot loop: render SVG → headless-browser PNG → look at the map → adjust.

A few favorite emergent behaviors, none individually programmed:

• Lakes: priority-flood treats below-sea-level depressions as water, so inland lakes appear with their own waterlined shores, and the largest earn names (The Bairasha Basin).
• Estuaries: rivers widen toward their mouths because accumulation grows monotonically downstream.
• Mountain passes: roads thread between glyph ranges because slope is the dominant Dijkstra cost.
• Realm borders follow rivers and ridgelines because crossing them costs extra.

License

Vellum's source code is released under the MIT License.

Maps you generate with Vellum are dedicated to the public domain (CC0): use them for anything, including commercial work, with no restrictions and no attribution required.

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For contributors

The house rules live in handbook/specs/, one file per area and every one of them normative. Read them rather than a summary here, since the summary is the thing that goes stale.