The Renaissance architect, moral philosopher, cryptographer, mathematician, Papal adviser, painter, city planner and land surveyor Leon Battista Alberti provided the theoretical foundations of modern perspective geometry. Alberti’s work on perspective exerted a powerful influence on painters of the stature of Albrecht Dürer, Leonardo da Vinci and Piero della Francesca. But his Della pittura of 1435–36 contains also a hitherto unrecognized ontology of pictorial projection. We sketch this ontology, and show how it can be generalized to apply to representative devices in general, including maps and spatial and non-spatial databases. 1 Through a Glass Clearly The Della pittura of the Renaissance artist and art theorist Leon Battista Alberti, dating from 1435–36, is the first modern treatise on painting. It defends a view according to which the proper goal of the artist is to produce a picture that will represent the visible world as if the observer of the picture were looking throug...