Merge

Merge is the union of shapes on one layer: overlapping or touching outlines on the same sheet are glued into one outline so the file matches the conductor that was meant.

Drawing is sloppy on purpose. Two rectangles that overlap look like one bar. A rule checker may still see a slit, a notch, or two widths. Merge makes the stored outline honest. It also destroys history. The two rectangles cannot be pulled apart after the outlines have become one polygon. Select a stitched power rail and the vertex count can drop from 40 rectangles to 3 outlines. A 2 micrometer overlap disappears into a single 10 micrometer-wide strap.

On the left the two rectangles still overlap as two outlines. On the right they are one outline.

Merge is a Boolean union with extra hygiene for holes, slivers, and touching corners. Shapes on different layer names do not merge. Touching is not always merging. Some tools want a true overlap. Merging the whole chip to clean it up can swallow a keepout drawn on the same number, or lose a pin marker. Merge the sheet that was meant. Touching shapes that still count as two pieces are overlapping is not merging. The cleanup that makes them one outline is merging polygons. And, or, and not on those outlines are Boolean AND, OR, NOT.