THEORY:

When the projectors (ex: line of sight of humans) from the source are parallel to each other and perpendicular to the plane of the object, for example a person looking at building, then the projection is called as an Orthographic Projection.

Isometric projections is a type of technical drawing where the three axes, i.e., x, y and z, are represented at equal angles (120 degrees) to each other. This gives a three-dimensional view where an object's depth, width and height appear to be in equal proportions.

Every point and every line in an orthographic view has a meaning. A point may represent a corner or an edge. A line may represent an edge or a surface. The meaning of each point or line should be interpreted by systematically referring back and forth from one view to the other. Simultaneously, the shape of the object as a whole should be visualized.

The most convenient method of drawing the isometric view of any solid object is the boxing method. 
In this method, the object is considered to be placed in a rectangular box having dimensions with maximum dimensions of the object along the three axes.
The edges of the rectangular box are the isometric axes and the surfaces of the rectangular box are the isometric planes.

The four basic steps for creating an isometric drawing are:

1. Positioning the object. Determine the isometric viewpoint that depicts maximum features of the object

2. Once the object is positioned and the viewpoint is decided, draw the isometric axes which will produce that view-point.

3. Construct isometric planes, using the overall width (W), height (H), and depth (D) of the object, such that the object will be enclosed in a box.

4. Locate details on the isometric planes. Darken all visible lines, and eliminate hidden lines unless necessary to describe the object.