In his drawing of the Church of Saint Spirito, Dosio used line to accentuate the patterned surface of the ceiling and differentiate it from the walls.
The ceiling and the walls in this church look similar, given that they both have a patterned surface, however, this surface was emphasized on the ceiling so as to make a visible difference between the two. The artist didn't want the whole inside of the church to look the same and made of the same material.