The placement of any element within the image frame, even a small one (see single point), divides the frame. For example, placing a one element dead centre in the frame automatically divides the frame geometrically in a 1:1 ratio in height and width. The number of sections, and the relative proportions into which the image area is divided is fundamental to any consideration of visual composition. There are an inconceivable number of division strategies; rectilinear or triangular, with the former the most common.
Uses ratios of whole numbers e.g. 1:1, 1:3, 2:3, most famously utilised in by Renaissance artists like Brunelleschi in architecture. This leads to static, relentless compositions.
Golden section or golden ratio
An ancient Greek division where the ratio of the smaller part to the larger part (small:large) is equal to the ratio of the larger part to the sum of smaller plus larger part (large:small+large). Algebraically, if the area of the small part is S and the large part is L, then S:L = L:(S+L). This works out as the ratio with the irrational number 1:1.618
Where the next number of the sequence is the sum of the preceding two e.g. 0,1,1,2,3,5,8,13...
In a real-world context, elucidation of the ratios of frame division in successful images tends to occur after the fact. The main exception to this is often-used and sometimes abused 'rule of thirds'; where two horizontal and two vertical lines dividing the image frame into nine equally-sized sections are imagined, and the subject is placed at any of the four intersections. It's common because it is easy to calculate and indeed, some digital cameras have an option to superimpose the rule-of-thirds grid on the viewing screen.