locus

In mathematics, traditionally the path traced out by a moving point, but now defined as the set of all points on a curve satisfying given conditions. The locus of points a fixed distance from a fixed point is a circle. The locus of a point equidistant from two fixed points is a straight line that perpendicularly bisects the line joining them. The locus of points a fixed distance from a line is two parallel lines running either side.

For example, a goat chained by a 3.5 m length of rope, attached to a peg in the centre of a field 6 m × 8 m, cannot move beyond the circumference of a circle 7 m in diameter:

The goat cannot reach the shaded area of the field.

Construction and scale drawings are often used to solve loci problems.