How to add a square grid as a layer?

[Caenwyr]

OH YESH I forgot to mention that for LARGE canvas you can still copy/paste groups of lines easily this way. OR you can also extend the lenght.. this is Just an opinion however. Something I found much more useful than a pixel grid.

Another way to recycle an existing grid made out of paths for a larger map than originally anticipated is to double it in size, copy the layer, and shift the second one half a square up and half a square to the right. Et voilà, a new grid 4x as large as the original, with the same mesh size!

Also, there are Photoshop brushes out there that have a pre-made grid. This one's pretty nice. Brushes are by definition raster data though, so you can't easily scale them up/down without messing up the width of the lines. So use with caution!