Isometric projection is utilized for representing images in three dimensions (3D) on a two dimensional (2D) surface. Isometric drawings are based around 30 and 120 degree angles. Isometric projections are more difficult to produce than oblique projections but they are more visually convincing and give the true scale dimensions of an object in the X / Y / Z axes. To create the visual effect, however, the shapes are distorted and rectangles become parallelograms and circles become ellipses and generally all shapes get smaller the further they are away creating a feeling of distance in the drawing.
Examples
A cube is drawn in isometric projection as follows:
To construct an isometric circle we first need to draw an isometric square with the sides equal to the diameter of the circle, and then construct the circle within it in 4 sections using a compass as follows:
Isometric dot paper
Isometric dot paper can be used as a guide when drawing. This paper has dots arranged across the page at 30o as an aid in drawing the correct angles. Isometrics is also quite isometric :P