A field of activity is a broad area of work or study that encompasses many different aspects. A SPHERE is a round object or area, and can be used to refer to a particular area of activity. A PROVINCE is a large area of land, and can also refer to a particular area of activity. A DOMAIN is an area of control or influence, and can be used to refer to a particular area of activity. A DEPARTMENT is a division of a larger organization, and can also refer to a particular area of activity. A TERRAIN is an area of land, and can also refer to a particular area of activity. Finally, PURVIEW is the range of authority or responsibility, and can be used to refer to a particular area of activity. All of these terms can be used to describe a field of activity.