Generating pattern-based estimated RC data with analysis of route information

A method and apparatus for improving physical synthesis of a circuit design is described. In one exemplary embodiment, preliminary routing information of nets in the circuit design is analyzed. The preliminary routing information includes track assignment information. Timing-critical nets are identified based on statistical distribution of the preliminary routing information of the nets. The identified timing-critical nets are assigned to a set of routing layers and removed from future net pattern matching. The remaining nets are clustered into multiple net patterns based on their physical attributes. The scaling factor for each net pattern is updated based on the scaling factor standard deviation and net length of the net pattern. Nets that are outside multiple standard deviations of a net pattern are assigned to routing layers. The scaling factors of the net patterns and the layer assignments are applied to the next phase of placement-based optimizations.