At the crudest level of engineering drawing, parametric design uses a method of linking dimensions and variables to geometry in such a way that changes to the values change the geometry as well and vice versa. The design file does not consist of raster lines, circles, arcs, etc. as in 2D CAD programs, but of vectors generated by dimensional and other data about what the desired end product. Therefore, as parameters are entered, drawings in both 2D and 3D are automatically generated from the geometry implied by the data entered. Combining simulation technology with parametric design principles allows engineers to design structures by manipulating 3D virtual models; if required, 2D construction documents can then be generated from the working model.

Expanded to incorporate the reality in which the structure or product exists, parametric design allows the engineer to focus on decision-making to determine the optimal form of a product given a customer's desired function. Analytical and experimental methods embedded in the design software rapidly model and predict the performance of each alternative, reiterating when necessary to assure that all candidates are feasible. It allows customer and engineer together to evaluate the behavior of each design alternative to quickly select the optimal. As cost information is one of the parameters included in good parametric design tools, trade-offs can be displayed and considered until the parties settle on the values of the design variables that satisfy constraints and maximize customer satisfaction.