Transistor Level is also known as “flat” extraction. Any cell placements are flattened
into the top cell.
Gate Level extracts parasitics for geometries within the top cell, down to the boundary
of the xcells. Xcells are specified in the file provided to the Inputs > H-Cells tab.
Hierarchical extracts parasitics for each identified xcell (not each cell placement) and
the top cell. All geometries have parasitics extracted.