How to image diagonals
That's difficult to image a diagonal without seeing a board. So, I thought how to image a diagonal. Of course imaging that depend on the person. Just for information.
Firstly, imaging three square's diagonals ( red ) on the 4 x 4 squares. That's easier for me to image it with another three square's ( blue ) . It's more important to recognize where squares are than imaging figure clearly.
Four square's diagonals
Imaging it with two 2 x 2 squares.
Five square's diagonals
At first, memorizing either end of five square's diagonal. And then imaging five squares with three square's image and 4 x 4 square's image.
Six square's diagonals
Similarly, memorizing either end of six square's diagonal. And then imaging six squares with three 2 x 2 squares.
Seven square's diagonals
Memorizing either end of seven square's diagonal. It might be the most difficult to image seven square's diagonal. I image it like the diagram below.
Eight square's diagonals
That's easy, right? Imaging that with four 2 x 2 squares.