Cutting and Lapping
Decreasing width and/or length on a pattern piece by cutting the pattern and overlapping at the area where a reduction is required. Lapping can be done through the whole pattern piece or just on one side, depending on the alteration required.
Examples
Image 1: This is an alteration done on the bodice front to shorten the length between the bust and the waist. The pattern piece is cut from the CF to the side seam, and the bottom piece is moved up the required amount. When making alterations like this to commercial patterns, you need to keep in mind the effect that the change will have on the adjoining pattern pieces. In this case, you would need to make a similar change to the Back Bodice Block; if you don't, the side seams of the pattern pieces won't match and you will have extra length in the back. In this case you will also need to true the side seam and the dart legs.
Image 2: This alteration is done for a Hollow Chest. In this case the lapping is not done symmetrically. The pattern piece is cut from the CF chest area to the shoulder tip, with the cut made to the seam line, not through to the cutting line. The lapping is done only at the CF. In this case the Center Front line will need to be "trued". No other pattern pieces are affected by this alteration.
