Metaphor: drawing a horse

I found myself amid of a major discussion the other day. When defining the scope of a project, should one also state things that are _out_ of the scope? Some people said that this would lead to wishful thinking and describing the whole world in the "out of scope" section. The others said that everything _in_ scope could never be described in adequate detail anyway so describing the outer world is the only way to go. So I got into thinking (considering I also had to present on the issue), ended up with an analogy:

Say you wanted to draw a horse and did something like this (art lovers, look away now):
It ain't pretty, isn't it? One could also use a different approach:

Isn't going to win any prizes also. But combine the two:

And you get something that is still ugly but at least gives a sort of holistic view of the animal. So the point is that you need both the inside-out and outside-in perspectives on a project to get a sufficient understanding of its scope.