The watertight geometry workflow lets you create body of influence (BOI) type refinement regions using the Create Local Refinement Regions task. One of the ways of creating a refinement region through this task is by using the “Offset Surface” type. Two types of BOIs can be created using the Offset Surface type: Boundary Layer Levels and Wake Levels. In this lesson, we will first learn how to set up the offset surface local refinement region for a selected object. We will then discuss in detail the two types of BOIs that can be created using this task — boundary layer levels and wake levels — with the help of an example.