You are the head of a large, city-government department, in a large city. This means that your agency/organization is a public/government agency (not a private organization nor a non-profit). This also means that your agency is not a National/Federal agency, it is not a state agency, it is not a county agency, it is not a regional agency – it is a large, city-government agency. If you do not know what constitutes a large city, look it up.