Polygon

A polygon is a closed chain of points that fills the space inside, the way a fence encloses a yard.

Most real factory shapes are not neat rectangles. A transistor island, a bent conductor, a liquid channel, or a letter on a board is a ring of corners. If a corner is in the wrong place by one tick, a rule check can fail, or a mask can grow a nick. Click a crooked metal shape and the editor highlights a loop of vertices, not a centerline. A typical island might be 3 micrometers by 1.2 micrometers with eight corners after a notch is cut for a contact.

The outline is an L: six corners, one filled shape, not a rectangle stored by two corners.

A four-sided special case is a box. A fat line stored as a centerline plus a width is a path. Many tools later turn that path into a polygon before a mask is written. An empty region inside the fill is a hole. Two overlapping polygons on the same sheet are still two loops in the file. Overlap is a picture until a merge makes them one piece of metal. The loop that is not a rectangle is polygons, the real workhorse. The four-sided shortcut is boxes are rectangles. Both live on sheets, which is what is a layout.