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Map Formats and Generation

How Mimir handles battle maps — from uploaded files to procedurally generated terrain.

Two Ways to Get Maps

Mimir supports two approaches to maps:

  1. Upload an existing map file (UVTT or image)
  2. Generate a map procedurally from a biome preset or YAML configuration

Both produce maps you can use in play mode with tokens, fog of war, and lighting.

The UVTT Format

UVTT (Universal Virtual Tabletop) is the preferred map format. Created by Dungeondraft and adopted by other tools, a .dd2vtt or .uvtt file bundles:

  • Map image — The rendered map as a PNG
  • Grid data — Cell size, offset, and dimensions so tokens snap correctly
  • Walls — Line segments that block line of sight for fog of war
  • Doors — Interactive wall segments that can be opened/closed
  • Lights — Light source positions with color and intensity

When you upload a UVTT file, Mimir extracts all of this automatically. Fog of war, line-of-sight calculations, and lighting all work out of the box because the wall data is embedded in the file.

Image Files

You can also upload plain images (PNG, JPG, WebP) as maps. These work for basic token placement but lack wall data, so fog of war is not available at all — the Fog and LOS controls only appear for UVTT maps. On image maps, the available tools are the Reveal Map toggle and per-token Hide from Players.

Mimir defaults to 70 pixels per grid square for image files. If your map image uses a different grid size, token snapping may not align perfectly. For best results, use UVTT format.

Procedural Map Generation

Mimir includes a map generator (mimir-mapgen) that creates Dungeondraft-compatible maps from a declarative configuration. Rather than hand-drawing every map, you describe what you want and the generator builds it.

Biome Presets

The fastest path: choose a biome like “forest,” “cave,” “desert,” or “arctic” and the generator produces terrain with appropriate textures, vegetation, and features. Presets encode the decisions a map artist would make — which materials to blend, how terrain should transition, what vegetation density looks natural.

YAML Configuration

For full control, write a YAML configuration that describes the map you want declaratively — dimensions, terrain layers, room layouts, features, and lighting. The generator translates this into the output format. See the Mapgen Reference for the complete YAML schema.

Output Format

The generator outputs .dungeondraft_map files — the same format Dungeondraft uses natively. This means generated maps can be:

  • Opened in Dungeondraft for hand-editing and polish
  • Exported from Dungeondraft as UVTT for use in Mimir (with full fog of war and lighting support)
  • Shared with other tools that support the format

Mimir cannot open .dungeondraft_map files directly — map uploads accept only UVTT (.dd2vtt, .uvtt) and image files. To use a generated map in Mimir, open it in Dungeondraft (a paid tool) and export it as Universal VTT.

Standalone CLI

The map generator also works as a standalone command-line tool, independent of the main Mimir application. This is useful for batch generation or scripting.

Why Dungeondraft Format?

Mimir chose the Dungeondraft format for several reasons:

  • Rich metadata. Walls, doors, lights, and grid data are all part of the format — exactly what a VTT needs.
  • Ecosystem. Dungeondraft is widely used in the TTRPG community, so maps created there work in Mimir and vice versa.
  • Editability. Generated maps can be refined in Dungeondraft before use, bridging procedural and hand-crafted approaches.

The Trade-Offs

Each approach has different strengths. UVTT files give the richest play experience (fog of war, lighting, doors) but require a map-making tool. Images are the most accessible — any map image works — but lose advanced features. Procedural generation is fastest for outdoor terrain and random encounters, but its output requires a pass through Dungeondraft (to export UVTT) before Mimir can use it, and complex interior layouts may need hand-editing there anyway.

The choice often depends on the encounter: a carefully planned boss fight deserves a hand-crafted UVTT map; a random wilderness encounter can use a generated biome; a map from an online artist works fine as a plain image for token play (no fog of war).

See Also