In a plane, a geometric figure defined by the union or the intersection of two half-planes whose boundaries intersect at a point *O* called the vertex of the angular sector.

- The radian measure of a salient angular sector is the real number \(a\in \left[ 0,\pi \right]\).The radian measure of a re-entrant angular sector is the real number \(\left( 2\pi-a \right)\) where \(a\in \left [ 0,\pi \right ]\).
- The degree measure of a salient angular sector is the real number \(\beta \in \left [ 0,180 \right ]\). The degree measure of a re-entrant angular sector is the real number \(\left ( 360-\beta \right )\) where \(\beta\in\left [ 0,180\right ]\).
- The gradient of a salient angular sector is the real number \(y \in \left [ 0,200 \right ]\). The gradient of a re-entrant angular sector is the real number \(\left ( 400-y \right )\) where \(y \in \left [ 0,200 \right ]\).