To get a view into the Cobb Gate circle and make the first version of my sketch of it, I stood in the middle of the street the busiest point in the contemporary trafficful town and let the vehicles find their way around me, which they did quite good-naturedly. (Try it; one thing borne in on you is how darn much traffic there is and what an unremitting noise it makes.) But even from this angle I couldn't properly see the area I was trying to draw or the various exits from it. That was why, to paint a better version, I had to levitate myself forty feet above the ground. (Any higher, and the sea horizon would have been off the top of the paper.)
Seriously, there is a more general point of which this is an extreme example. The shape of a scene that you contemplate in your mind is seldom, if ever, the same as the scene that objectively maps itself on your eyes. I know that the Cobb Gate is roughly a square area with a traffic circle in it and a way out around the corner to the left and a way out to the right and a way out down the jetty. That is its Platonic form, the image of it in my mind as I walk into it. But there is no one point on the ground from which I can physically see all these elements of it. From the sidewalk on the left, I can't see the opening around the corner to the left, and so I step out into the street. But even then, the scene stretches too far from left to right and is too compressed vertically (the square area isn't seen, only a horizontal smear of its contents, mostly cars); and I can't see the jetty at all, because it is down behind the sea wall. I have to levitate forty feet upward to see something more like the map my mind sees.
The same is true, perhaps more subtly, of other scenes. My drawing of a scene is unlikely to map exactly onto any photograph of it. The most typical of the distortions, in which drawing follows mind, is in scale: we think of recognized things in the distance as larger, that is, subtending larger angles on the eye than they actually do. And vertical exaggeration: we see, and draw, buildings as taller, streets narrower than they are. It is as if we hanker to live in a world with more up-and-down and less flat expanse, rather than this world where distances are measured in kilometers and heights in mere meters. And horizontal contraction: one wants to reduce the uninterestingly great span of hedge or building between two diverging paths, or the uninteresting span of wall between the views out of two windows in a room.
Other differences (it is hard to separate them) of mind-drawing from photographed-objectivity:
The mental image of a scene is partly the map of it, as if you are not only confronting it but looking down on it.
The mind (and the drawing) may include elements that are not really in view simultaneously. As I walk toward a crossroads that I know is approached by a steep descent around a curve, I see the descent and the curve and the crossroads at separate moments, and then the beginning of the road that opens to the left, but they are all in my image of the crossroads and should all somehow be present in a sketch of it.
Perhaps the best way of summing up the mental image is that it is a composite of plural images: numerous mental snapshots go into the making of it. In this way, it is like the knowledge of a friend's face, which you know better than a photograph can show, because you have seen in it in motion and in differing moments. This is part of why pictures made from photos (of which I have done a few) have a flatness as compared with pictures made directly from the scene.
Oh, and besides including a drawing can exclude: cables, signs, trashcans, drainpipes, scaffolding, cars! And can show impossibilities such as a stoplight red, yellow, and green at the same time.
(More of this essay possibly to come.)