An LSI designing system includes a memory;, a database configured to store
a layout layer definition file, and a control section configured to refer
to the database to build up a plurality of layout layers in the memory
based on the layout layer definition file. The plurality of layout layers
are provided for extending directions of patterns in one of physical
layers of an LSI to be formed. The control section divides each of the
patterns into pattern structures based on the extending directions, and
assigns each of the pattern structures to a corresponding one of the
plurality of layout layers.