>>5736135Not him but if I'm not mistaken, and if I understand the meaning of your "angle of projection", basically you choose a vanishing point (which will also naturally gives you the horizon line).
The, you put your base line where you find it eye-appealing to be, according to what you want to draw.
The horizon line is the line where your eyes are, so for instance in Loomis' drawing, where you to draw people on that grid, they would all have their eyes on the horizon line (more or less, depending on their height relative to you). In this setting, this make quite big people, and this is not a great setting for a cityscape with an emphasis on buildings.
There's also something called the cone of vision, which again IIRC is basically a way to crop a theoretical perspective grid to match something pleasant to the eye. Some paintings just try to "embed too much perspective", it's unappealing. I suppose >5734555 is an example of that.
Hope it helps, but take my words with a grain of salt, I'm rusty of non-intuitive perspective.
