Complex systems and large installations should operate reliably without interruption or degraded performance due to electromagnetic interference. Intolerable electromagnetic interference requires both a source for creating a disturbance and a victim for which electromagnetic disturbance is intolerable. Disturbances may travel over cables or through the air as electric or magnetic fields or as electromagnetic waves. Both US Federal Communications Commission and European Union directives relate the electromagnetic compliance of equipment to the intended environment. The risk of electromagnetic interference is low when the attributes of the installed equipment and its zone coincide. The electromagnetic phenomena in overlapping location classes blend, and zoning might be appropriate to enable mitigation measures. A zone is therefore a volume, limited by physical boundaries, and described by its electromagnetic phenomena. The zone compatibility matrix is used to summarize the information about the user environment and the intended environment in order to detect possible mismatches which lead to risk of noncompliance.