Definition - Depth

Depth: 

The distance from the top or surface to the bottom of something.

My own definition:

How deep or long the length/width of an object is.

Depth can be shown by taking the photograph close to the bottom of the main focus; in this case, it's the ground. By putting the camera close to the ground, the buildings look more powerful, making the street look longer and emphasises its depth.

In this picture, the port seems to get smaller and smaller as you move your eyes from the bottom of the picture to the middle. This shows depth because it brings your eyes on a journey, making it seem long which puts even more stress on the depth of this scene.

The photographer who took this picture zoomed into this piano to make it look bigger. They have done this to show even more depth to this object - probably more depth that it actually has.

This picture has been blurred deliberately to accentuate the depth of this scene. By using this technique, the viewer is lead to believe that the background is too big to be sharp enough for them to see it clearly in the picture.