In Revit, a building information model is organized as a project, with the project file containing all the model’s data. The fundamental elements of a project are graphic components, which are structured into four hierarchical levels: Category, Family, Type, and Instance.
The first level is Category, which includes various types of building elements such as walls, columns, doors, windows, structural components, pipes, equipment, and more. Each category has predefined roles within the software, allowing all elements of the same category to be selected easily through filters. Every component in the model belongs to a specific category—for example, all columns are grouped under the “Columns” category. Categories can also have subcategories to allow for more precise control; for instance, “Structural Columns” is a subcategory within the “Columns” category.
The second level is Family, which represents a group of elements sharing common behaviors and characteristics. Each family must be assigned to a specific category. Families can be considered as collections of geometric shapes—for example, the column category can contain cylindrical and square column families, differentiated by their cross-sectional shapes. This classification helps organize components into meaningful groups.
The third level is Type (also called Style), which refers to variations within a family. Different types can have distinct materials, sizes, or other properties. For example, within the cylindrical column family, there might be several types with varying diameters and materials. Each unique combination represents a different type within the same family.
The fourth and final level is Instance, which refers to the actual placed elements in the model. Instances are specific occurrences of a type, concretizing the type’s definition in the project. For example, a building may have multiple identical columns placed in different locations; each of these is an instance of the respective column type.
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