All sizes of negatives and printing papers are arbitary, and determined by the manufacturer. The real shape is the circular image by the lens. I have to compose within that circle. Therefore, the problem pf square versus rectangle does not disturb me. It is easy to compose a horizontal or vertical image within a circle. It is possble to compose this either when taking the picture or later in the darkroom. Many times my final picture are square. I do not allow the proportions of the paper to dictate my compostion. I cahnge the proportions if they do not fit my idea of what the picture should be.