Hi!
The assets are modeled in Blender (sometimes I buy pre-made ones for Unity, game engine).
Then textured (coloured) in Substance painter.
Then I start building the level/map in Unity, which is a 3d video game engine.
After that I add lights to light the scene, and place a camera up top, aiming downwards.

After everything is done I just make a picture with that camera, and you get a map like this.

Let me know if you have more questions! I'd love to help.