The PATH is one of the two base geometric entities used to describe the layout (the other being the BOUNDARY)
The PATH consists of two or more vertices that describe the center point of a line. The path normally has a finite width. This is a straightforward concept except for the bends in the path and the start/end of the path.
Number of Vertices per Path
The GDSII specification limits the number of vertices to 200.
Most GDSII readers can support a much larger number of vertices. The maximum is 8191 vertices based on the two bytes available in the path record that describes the number of XY records to follow.
The GDSII specification says nothing about how the bends in a path should be rendered. For 90 degree bends there is no confusion. However for bends with acute angles most rendering algorithms assume some amount of mitering - the exact formula for the miter will vary from implementation to implementation.
The path record has a flag that indicates the nature of the start and end (known as the end caps.) There are three standard values and a fourth flag that indicates a custom value.
1=Half Round Extension
2=Half Width Extension
Self intersecting paths (a) should not be written out to GDSII. Some tools that read GDSII will correctly interpret them but many will generate unexpected results (b) or even crash.