Prismatic Plains

Prismatic Plains is a browser-based hex worldbuilder for DMs, mapmakers, and anyone who wants to discover strange terrain by shaping the world one hex at a time.

Push a desert into a holy coastline. Freeze a lake into mirror-ice. Raise a lonely peak above the clouds. Corrupt a peaceful marsh until something starts living there. Every modifier changes the hex

How to Play / Build

➕ Left Click a hex to increase the selected modifier
➖ Right Click a hex to decrease the selected modifier
💠 Click + Drag across hexes to select multiple cells
🖱️ Middle Click or press tab key to lock selected hexes
🌠 Shift key to make selected hexes mythic; Which bookmarks it for the game master, and changes the name. You should prep hard for these locations. Rename these to your liking.
🖌️ Choose a modifier brush on the left, or directly edit a selected hex from the right panel

⚙️ Rename a single selected hex cell
🐉 Edit the dangerous encounter chance for a selected hex
📏 Set the map scale with 1 Hex = Miles
🧮 Select multiple hexes to measure their total area in mi² and km²
⬇️ Export and import your maps as readable JSON files

🖨️ Print for home use! Many toggle options. Please reach out if you need something more.

Discover

The world tracks how many unique terrain names you have discovered. Try extreme combinations, locked impossible borders, holy lakes, infernal cities, monster lairs, roads, wildlands, ravines, sandbanks, and weird coastlines.

Technical Notes

Each hex stores its modifiers plainly:

{
  humidity: 0,
  temperature: 0,
  sanctity: 0,
  population: -35,
  elevation: 0
}

Every modifier uses a signed -100..100 scale. sanctity is the glory/corruption axis: negative values are corrupting or infernal, positive values are hallowed or celestial, and 0 is natural.

Terrain is resolved through layered rules instead of one giant hardcoded chart. A high-population corrupted lowland can become something very different from a low-population corrupted mountain, because each terrain rule checks ranges across multiple axes.

The system also adds contextual tags after the base terrain is chosen. Roads are derived from settlement paths. Monster tags appear when danger rises above the threshold. Locked hexes can preserve impossible terrain borders, letting you place deep trenches beside sacred peaks or frozen lakes beside burning wastes.

Everything runs in the browser with HTML, CSS, and JavaScript only. No server is required after the page loads.