# Floorplanning with PDC Commands

You can use the define_region PDC command to create a rectangular or rectilinear region, and then use the assign_region PDC command to constrain all the macros to that region.

Floorplanning reduces the risk of placement conflicts of the blocks at the top level. If you do not constrain your block placement, its components may be placed anywhere on the die.

It is also important to consider the placement of all Block Interface Instances at the boundaries of block regions. This facilitates the interconnection of the block to the top-level design. If the block is highly optimized (densely packed), there may be no routing channels available to connect to any internal Block Interface Instances. Placing all interfaces at block boundaries helps you eliminate routing congestion and failure.