These pages are for explaining geometry topics, with a focus on tools for 3D art and particularly level design.
I got interested in how BSP map compilers work, and had to wade through a bunch of different resources to figure it out. This page aspires to contain all the information you need to build some basic level compilers, capable to taking a map from something like Trenchbroom and turning it into geometry that you can use in your own custom tools.
In order to make much progress understanding this geometry, you'll need to know some basics of vectors, and ideally have a good intuition for them. That summary page explains operations like dot products and projections, or cross products and normal vectors. Terms should always have links to their explanations!
Brushes
Learn about plane equations for representing lines and planes. With planes, we're able to define convex solids which are extremely computationally convenient to work with, and not too bad as a user interface.