# 'upper-left corner' or 'top-left corner'?

In a square, which is the correct term: 'upper-left corner' or 'top-left corner'?

To be more specific: in the context "the x-coordinate of the upper-left/top-left corner", which should I use?

I would interpret "top-left corner" and "upper-left corner" as both meaning exactly the same thing, and would use other words to differentiate between nuances. For example:

• in the top/upper-left corner would imply an area within the square.
• near the top/upper-left corner would imply an area near the corner, which may be inside or outside the square depending on context.
• at the top/upper-left corner would suggest the vertex itself or as close to it as you can get, again, inside or outside the square depending on context.
• etc. ...

Even if there are subtle differences between top and upper in this context, it would be a brave author who would rely on the readers interpreting the subtle differences exactly as expected. If there is doubt as to the clarity, then amplify it to make it clear. Sometimes 6 words or 10 words are better than 3!

I interpret "top-left corner" as the corner vertex, and "upper-left corner" as the area in proximity to the corner vertex. This follows from top's meaning as the extreme element, and "upper*'s as the relative element, of a comparison of heights.

Top:
1.The highest or uppermost point, part, or surface of something.

Upper:
Situated above another part.

However the distinction is subtle, and even my own writings is probably not 100% consistent.

• I think both refer to the same vertex. The word "corner" in a mathematical sense should unequivocally mean the corner vertex. "Upper corner" is simply to distinguish it from "lower corner". Commented Aug 18, 2013 at 17:45
• @KaiserOctavius: Just because the context is a square doesn't make it mathematical; it could as easily be a Windows window. Commented Aug 18, 2013 at 18:03

I think 'top-left' is clearer than 'upper-left', but in either case there is slight room for ambiguity insofar as a reader could interpret it as "somewhere around the top left". For complete clarity, I would suggest 'top-left vertex' - assuming your readers understand what you mean by 'vertex'.

The Microsoft Manual of Style manual specifies terms such as "upper-left" and "lower-right".