2D Shapes - Circles
A 2D shape is a geometric figure that has only two dimensions, width and height. 2D shapes are flat and have no thickness, they can be drawn on a plane and can also be called Plane Shapes. (A plane is a flat two dimensional surface. like the surface of a piece of paper).
Circles, squares, rectangles and triangles are all examples of 2D shapes.
We classify 2D shapes by the number and size of their sides, the number and size of their angles, and by the relationships between the sides and angles.
The first 2D shape to look at is a circle - it has 1 curved side with no angles. It is described in terms of the circumference, which is the distance around the circle, its radius, which is the distance from the centre to the outside of the circle and the diameter, which is the distance from one side of the circle to the other passing through the centre. So the diameter is twice the length of the radius.