Which element in Revit is primarily used for defining the layout of spaces?

The element in Revit that is primarily used for defining the layout of spaces is grids. Grids serve as a framework for organizing the overall design of a project, providing reference points that help in placing other elements such as walls, columns, and beams. They establish a system of alignment that dictates the proportions and relationships of spaces within a building, allowing for systematic arrangement and ease of coordination among different design components.

While walls, floors, and roofs are essential for creating the physical boundaries of spaces, grids help define those spaces' overall configuration and layout. They are crucial during the early stages of design, enabling architects and designers to visualize and plan the spatial organization effectively.