A top-down floorplanning automation tool, PIAF, which combines knowledge-based and algorithmic techniques, is presented. PIAF designs floorplans by estimation, planning, and successive refinement using a strategy that separates the floorplanning process into either knowledge-based or algorithmic phases. The former implements qualitative reasoning, while the latter addresses fast quantitative processing. This strategy eases the acquisition of expert knowledge as subdomains become more narrow and produces results comparable to those of experienced integrated circuit designers in a fraction of the time. An example is given to illustrate PIAF's operation.