Compared to the intricacies and complexity of the second iteration, describing the goal of the third iteration is simple: perform the study. This step is largely about aggregating all of the questions and answers you have accumulated and using that information to gather data, construct models, and assess the results. Steinitz asserts that the limited explanation about the third iteration is no way a reflection on how much time and effort the geodesign team will spend working through this phase, especially because the nature of the third step is that it will likely be repeated several times based on feedback from stakeholders.
Up to this point, the geodesign framework has been described in a strict linear fashion. Throughout the process, you have been asked to make decisions, often without as much information as you may have preferred. Remember how little information you had to shape the first representation model, compared to the well-informed study you have now? Armed with this new knowledge, the team might want to step backwards and rethink earlier questions and models. Perhaps the team observed a behavioral process that was not fully captured within the representation boundary (which could necessitate a change in scale for performing the actual study), or the amount of change expected will include additional, unforeseen impacts (might indicate a change in scope is needed). These changes may or may not alter later questions in this last iteration of the framework; the goal is to enable the approach to the overall study to better address the problem. The freedom to move forward and backward in an organized manner is the strength of a structured framework.