A Top view displays the model from the top:

• the xy plane is parallel to your screen (as in a 2D model).
• x is positive from left to right (horizontally).
• y is positive from bottom to top (vertically).
• z is positive toward you, perpendicular to the screen.

While, for a Bottom view:

• y is positive from top to bottom (vertically).
• z is positive away from you, perpendicular to the screen.