Sectors

A sector is a part of a larger whole that shares common characteristics or functions. The term is used across disciplines to denote a subdivision of a system that interacts with other parts while retaining some degree of autonomy.

In economics, sectors classify economic activity. The primary sector covers extraction of natural resources (agriculture, mining); the secondary sector covers manufacturing and construction; the tertiary sector covers services (retail, finance, transportation). Many classifications also include the quaternary sector, focused on knowledge-based activities such as research and information technology, and the quinary sector, involving high-level decision making. Sector shares are used in national accounts and economic analysis to track growth, productivity, and employment.

In geometry, a sector of a circle is the region bounded by two radii and the arc between them. Its size is determined by the central angle. If the angle is theta radians, the area is (1/2) r^2 theta and the arc length is r theta. When theta is in degrees, area equals (theta/360) pi r^2 and arc length equals (theta/360) 2 pi r.

Beyond circles and economies, sector is used in planning and organization to describe a defined area or function within a system, such as a market sector or a sector of a grid. The term emphasizes boundaries and delineation rather than a single unit.