The focus on the tree in this picture defines emphasis.

The focal point is the main emphasis or main focus in a picture.

The difference and shading un this picture defines contrast.

The chess piece is focused and set aside to itself in this picture defines isolation.

The piece of art centered in this picture defines "objects in the center."

The the railing is implied lines going in one direction causing the ocean and the sky to become the focal point. This picture defines convergence.