Floorplanning large designs with many hard macros and IP blocks of various sizes is becoming an increasingly important and challenging problem. This paper presents a global floorplacement method that combines a hierarchical simulated annealing floorplanning method with a partitioning-based global placement technique. A novel area migration method formulated as a min-cost, max-flow network flow problem is used to improve area utilization, and provide a communication mechanism between the partitioning engine and the placement method for better design quality. The network flow area migration method can be used in managing incremental changes in the design as well. Our global placement wire length is 12% better than the detailed placement wire length of a previous work, while our global placement is almost 8 times faster than their global placement.