Depth compression — where it appears
The eye taken to infinity
A parallel projection is a photograph from infinitely far away with the lens lengthened to match. That is not an analogy — it is the limit, it can be watched happening, and it explains why a long lens flattens a scene and why an isometric drawing has no viewing distance to state.
A picture with no size–distance signal
In a system with no diminution the drawn size of an object falls at exactly zero pixels per metre, so nothing in the picture says how far away anything is. Depth has to be carried by something else, and what carries it is height on the page — linearly, and without a horizon.
What perspective gave up
The field ends by turning its own battery on the system it has been comparing everything against. Four quantities a pinhole destroys that the other systems keep, each measured on this site's own machinery, and each the price of the one thing perspective has and they do not.
Named alongside it
The objects these essays reach for when they reach for this one.
Drawing systemParallel projectionPicture planeStation pointViewing distanceArea scalecentre of projectionDemonstrationDepth cueDiminutionForeshorteningHorizon