I think you are thinking of a fusible product with a grid printed on it. I have used it to make a watercolor quilt wallhanging (the top is all squares, all the same size). You can buy it at JoAnn's. You need to lay your squares down in the order you want them, then use your iron to fuse them in place, bit by bit. Once that's done, you simply fold the top on a line, rst, and stitch the seam. Then fold on the next line and stitch that seam. Once you have all the seams sewn in one direction, you have to snip the seam allowances in all those intersections so you are able to repeat the folding/seaming in the opposite direction. Does this sound like what you had in mind?