This definition is a representation of the concept of an identified discrete almost homogeneous geological feature with either an irregular solid or 'Yabuki' top surface shape or a regular voxel cubic shape. A stratum is represented as a discrete entity, specialized (sub-typed) from IfcElement. A stratum can be broken down into smaller entities if properties vary across the stratum or alternatively properties can be described with bounded numeric ranges. A stratum can carry information about the physical form and its interpretation as a Geological Item (GML). The shape representations used should correspond to the sub-type of IfcGeotechnicalAssembly in which it occurs.