This study explores the value of visualizing the prototyping activities in a new product development process from idea to production. Through a case study of a hardware startup, we present a retrospective and longitudinal study of their prototyping processes, from early idea to the introduction of several product generations to market. We call the visualization technique ProtoMapping and we use the qualitative and quantitative data captured by the ProtoMap to understand how prototyping strategies change over the course of product development processes. Specifically, we focus on the prototyping of parallel concepts, iterations of concepts, manufacturing processes used for prototypes, prototype media, prototype tests, as well as prototyping of isolated or integrated systems. Based on this longitudinal analysis, we present a number of insights that were possible to uncover with ProtoMapping. We observe how parallel prototypes of isolated systems can be used to explore the solution space and later be synthesized into prototypes for integrated systems. Furthermore, we understand how the need to scale up production can lead to increased prototyping activities, as several parts of a product must be redesigned. This study illustrates the utility of a retrospective visualization approach and serves as the first step in formulation of generalized guidelines for prototyping strategies in holistic product development.