A structural irregularity that is observed in the plan (horizontal plane) of the building. If more than one plan irregularity is observed, the primary plan  irregularity is that deemed to be the most significant in terms of affecting the building’s seismic performance, and the secondary plan irregularity is that deemed to be the next most significant. If there is only one structural structural irregularity observed, the term "No Irregularity" will be used by default