Updated 2017-12-05
Map building requires using Hammer, included in the Dota 2 Tools. Hammer is a tool used by all Source games including Half-Life, Team Fortress, and of course Dota2. Hammer also relies on the use of Prefabs, Tilesets, Materials, Models, Particles, Sounds, etc. Maps are not only for designing the game area, but are also where prefabs, tilesets, and 3D splash screens are built and stored.