While I’ve been working on Aerill, my own fantasy extraterrestrial planet, I’ve come across a number of awesome, free, web-based tools to help realistically generate or view your planet’s surface.
Fractal World Generator by drow – https://donjon.bin.sh/scifi/world/
Quick and easy to use; takes a minute to load the generated 2D map on a new page, but it also provides you with randomized planet aspects such as the physical dimensions, gravity, atmosphere, and other fun inspirational thoughts. Obviously there is no obligation to use these, but if you want to make sure the physics are plausible, this has got you covered. The generated 2D map is only 800 x 400 and only comes in full topographical colors, which can be great if that’s all you need, but if you want to create height maps or high-resolution renders of your planet, you’ll need to edit the image.
Procedural Planet Generator – http://wwwtyro.github.io/procedural.js/planet1
My personal favorite surface map generator, because it provides your map in color, bump map, opacity map, and relief views. It can take a good amount of time and resources to load, especially at higher resolutions.
Harder to use, requires more fiddling with the settings under Surface > Noise to get the look you desire; I played trial-and-error with the Noise settings for quite a long time. Click “Randomize Seed” or “Randomize All” to generate a new map. When you find one that you like, raise the resolution up to 2048 or higher and save the generated map images.
This tool was used to create Aerill’s surface map!
PlanetMaker – http://planetmaker.wthr.us
This tool is a very detailed outer space scene creator, but it does not let you generate a new surface map. It has photo-realistic surface maps of real planets built-in, but you cannot really fiddle with the appearance of them, so you will want to bring your own pre-made map. Instead, it lets you play with more of the astronomical elements and view your world in beautiful, realistic high-definition. You can import your own surface map, specular map, height map, and bump map for a stunning look at your world. This tool also lets you play with sunlight angles, including sunlight at a particular Earth day and time, so you can figure out which parts of your world will be in each time zone, and create as many moons as you want.
Map to Globe – https://www.maptoglobe.com
This excellent, fast, and simple tool lets you import a map to view on a globe and also generate new maps. Generation options are fairly limited, but it works great and allows you to download the full 2D projection in high resolution in a TON of different projections for realistic maps that your inhabitants might actually use. It’s also great for quickly viewing your map textures wrapped around a globe without too many frills, which is vital for understanding how close your continents are to poles, each other, and in terms of actual relative scale. Loads super fast, and works great on mobile devices. Does not have features like sunlight angles or moons, which is great if you want clean images of your planet’s surface without stuff in the way.
BONUS: Normal Map Online – https://cpetry.github.io/NormalMap-Online/
This amazing, startlingly-fast online tool lets you create a normal/specular map from a black-and-white height map, which can then be used to give dimension to the 3D surface of your planet. It also contains tons of useful information about how normal maps work and how to make your own!