Organization is just the use of the space on the page. It's how you place things on the page and how that effects the consumer. Placing things so that it is put in a meaningful location to either draw the eye, or give the eye a break with blank space.
Proximity is the arrangement of the images or text in correspondence to the rest of the page. Kind of going hand in hand with organization, proximity however focusses on the area more or less around the items on the page as opposed to their actual placement.