Very true. I did not originally create this map with the border in mind. Hence, I didn't bother too much about configuring the height and width of the original canvas in such a way as to allow for the later insertion of a checkered grid. The original canvas size was 2764 x 2000 px. Later, when I decided I did want to add a border that contained a checkered-like set of neat lines, I realized my mistake: the canvas area was just the wrong size for what I wanted to do. I chose to go ahead with neat-lines anyway. I made a selection of the original canvas and converted it to a path. Then I expanded the canvas size, and stroked the new canvas with a checkered stroke, resulting in the odd corners you see in my map. This technique should still work fine for a map that is formatted differently than mine though (e.g. a map with a canvas size of 2600 or 2800 by 2000 could use a checkered stroke, setting the size of each box to 100px, and end up with square corners).