Mapgen4 Procedural Map Generator

Pick a starting seed, then paint mountains, valleys, and oceans on the map! It will simulate evaporation, wind, and rainfall to determine biomes and rivers.

Play with the sliders to change the simulation and style. For example, try decreasing raininess slider to see how reducing rainfall will make rivers dry up, or try decreasing lg_min_flow to see more small streams.

Treat this as a tool. Everything you create with it is yours to do with as you please. Credit is appreciated but not required. Suggested tag: #mapgen4. Download high resolution image (doesn’t work on all platforms).

Goals for this project:

• A hand-drawn inspired look. If you look at maps from Lord of the Rings and other fantasy settings, you’ll see the rivers and coastlines are top-down but the mountains and trees are side view. The map above is rendered in full 3D (try the rotate_deg and tilt_deg sliders!) but I used a custom projection and outline to more closely match a hand-drawn map.
• Being able to paint your own features on the map. With procedural generation we usually let the system generate everything. I wanted to generate something (mountains, valleys, oceans), then let you change those things, and then generate the rest (biomes, rivers). Maybe in a future version also let you paint the biomes. Making the map paintable also meant I needed to make it fast.

Status of the project: Finished, source code available^[1], but the project is mostly inactive. I made some code changes in Apr 2023, with slightly higher resolution maps, but the maps won’t exactly match previously generated maps. I have a series of blog posts^[2] about this project:

• [2018] History^[3] of the project
• [2018] Elevation^[4] to match the desired look instead of tweaking the look to match the elevation
• [2018] Distance fields for elevation^[5]
• [2018] Multithreading^[6] to make it run acceptably fast
• [2018] Fixing the appearance of rivers^[7]
• [2018] Revisiting distance fields^[8], which didn’t work out like I hoped
• [2018] Rainfall^[9], biomes, evaporation, wind
• [2018] Rendering with an oblique projection^[10], not the standard rotate+translate+scale
• [2018] Rendering outlines^[11]
• [2018] Some bug fixes^[12]
• [2018] River representation^[13] with binary trees
• [2022] Experiment: animated version of the map, but no longer paintable
• [2023] Rewrote the underlying geometry library^[14]
• [2023] Fixed several geometry problems with the edge of the map^[15]
• [2023] Added rendering of the side of the map^[16], which I think looks pretty cool, but most people will never see it
• [2024] Research: adding labels to maps
• [2024] Rewrote the mouse/touch handlers to work better
• [2025] Rewrote the renderer, making the page load faster
• [2025] Experiment: quick shape explorer
• [2025] Experiment: mapgen2 + mapgen4 hybrid
• [2025] Experiment: trade routes
• [2025] Experiment: finer control over elevation
• [2025] Rewrote the river renderer, making the rivers a little bit sharper
• [2025] Rewrote the terrain renderer, and added a mountain_folds slider

Also see my project from 2010^[17], where I started developing these techniques. There are lots of things that could be added on top of the underlying delaunay+voronoi structure, like towns, trees, biomes, seasons, nations, watersheds, etc. If you’re interested in adding these, take a look at the source code, and feel free to email me. One day I might work on a mapgen5 that explores some more ideas on top of this.