Devblog 11 - Marrying the building system with the terrain - Part 1
In minecraft the construction system is very simple, since any face of a block works. In our case it is not like that.If you remember, to generate the terrain, we have joined the bricks into a single mesh / model. So when we click to build on that model, we know that the player is looking at a piece of land. But not at which brick exactly.

Source and More information: Devblog 11 – Marrying the building system with the terrain – Part 1

Author: indieDB.com