The 2016 National Occupational Classification (NOC) system was used by Federal statistical agencies to classify workers into occupational categories for the purpose of collecting, calculating, or disseminating data. All workers were classified into one of about 500 unit groups according to their occupational definition. To facilitate classification, unit groups are combined to form about 150 minor groups, about 40 major groups, and 11 broad occupational categories.
The hierarchy of the 2016 release of the taxonomy was Broad occupation category (1 digit) > Major Group (2 digit) > Minor Group (3 digit) > Unit Group (4 digit).
Example
3: Health occupations (Broad occupational category)
32: Technical occupations in health (Major group)
322: Technical occupations in dental health care (Minor group)
3222: Dental hygienists and dental therapists (Unit group)
Upon the release of the 2021 version of the NOC taxonomy, the hierarchy is Broad occupational category (1 digit) > Major group (2 digit) > Sub-major group (3 digit) > Minor group (4 digit) > Unit group (5 digit).
The NOC version in Lightcast data was updated to NOC 2021 in June 2023.
More details are available here:
https://noc.esdc.gc.ca/?GoCTemplateCulture=en-CA