Now I'm in a quandary - between the two of you, you have the answer. I'll let you fight each other for the next question.
As people tend to assume that light comes from directly above them, cartographers light their maps with the sun positioned above the map, which makes sense. But, as art teachers would attest to, hill shading (and in my experience, most still life paintings) follows the convention of top left lighting because of a quirk of human perception - using any other directional light source causes multistable perception illusions - which cause the features of a map to appear inverted.
Try explaining that to primary school kids,as I've had to!!