When creating a pattern for a garment, I like to map the style lines and design details to landmarks on the body. It helps me grade the pattern appropriately. For designers, mapping the design can be helpful to envision how the design will look in different sizes and create proportions that fit well.
What I mean by mapping the design to the body is that I consider how each seam, design detail, and style line will fall on the body and what area of the body it will grade with. Darts that point towards the bust will grade with the bust point. The top of the armhole (where it meets the shoulder) sits on the shoulder tip and will grade with the shoulder.
Where on the body a detail falls and what part of the body it grades with are often the same, but not always. For example, does the top edge of a wide waistband on a dress grade with the waist or the underbust line? It depends on how tall the waistband is. Straps on a tank or sleeveless top might grade with the shoulder, but they might grade with the neck width. It depends on the style and design intent. It is particularly helpful to map the design to the body when the placement and the body grade landmark are different like this.
Even if you’re not the one doing the pattern or grading, mapping the design to the body will still help you design with different sized bodies and proportions in mind so you get a consistent look across your whole size range.