All you need is you, a class and a playground. Easy!

Loci around a single point
You stand in the middle of the yard and the class must all stand 2m away. Hopefully you will end up with a circle of radius 2m. Discuss why this happens.

Equal distance from two lines/Bisecting an angle
Find part of the playground which has two edges, ideally at 90 degrees. The class must stand the same distance from each edge – this should look like an angle bisector. Discuss.

Locus of a line
Get a few pupils to stand in a straight line. Everyone must stand 1m away from them. Discuss why the lines are parallel and the ends are semi-circles.

Locus around an object
Repeat the previous task around an object eg building, bench. Why do right angles produce quarter circle loci?