Rendering is based on normals direction

[GANys]

It looks like the viewer expects normals to be pointing outside only to render surfaces ("polygon oriented CCW when viewed from outside", dixit Hugo Ledoux).

An improvement might consider rendering surfaces either directions.

Currently, it looks a bit weird even if buildings are consistent.

Updtate : this effect is called "Back-face culling". Its purpose is to occlude faces which normals are not directed towards the exterior of the Solid. I leave it here as people might encouter such a problem also.