In one embodiment, a user interface system based on a treemap-type presentation includes a processor and a memory. The processor is operative to store data for items which can be invoked, generate data for a user interface screen having regions arranged according to an arrangement, at least some of the regions being different sizes and being arranged according to size order, assign at least some of the items to the regions, receive user selections from an input device, determine which item is being selected for each user selection, refresh an assignment of the items among the regions of the user interface screen so that even though the assignment of the items among the regions is changed as a result of the refreshment, the arrangement and sizes of the regions in the user interface screen remain unchanged. Related apparatus and methods are also described.