Parametric Design is a design system that associates parameters to the geometry of a design.
The design can be simple or complex. Parametric design is particularly powerful when parameters form relationships with other parameters. For example, changing one parameter, say length, may change many others because it is linked in relationship with many other elements.
A simple example is the relationship between two sides of a rectangle. By creating a formula that describes the rectangle (Width by Length equals Area or W x L=A), we can create a parametric relationship between some inputs and a rectangle.
Let’s say the rectangle has a fixed area of 12 meters. We can adjust the width across a range and the length is adjusted so that the area is always 12 meters. Length = 6m, then the width must be 2m. Width = 4m length, must be 3m.
When you start adding more and more parameters and relationships the model becomes exponentially more complex, but it also becomes more useful. So, in creating an architectural design, we can take the rectangle above and add a dimension to it. You now have a box, If you give that box a thickness, you have walls, a floor and a roof. Give each of those a different parameter for example wall thickness = 120mm then, if you ever have to change a parameter, for example, width of the original rectangle. everything else moves with it.
At a practice level, Parametric Design allows for design changes much later in the design process without the adverse consequences, and more importantly it can allow for design flexibility and resilience. This means you can reuse designs again and again even when the fundamental constraints change.