Manifold Absolute Pressure

The MAP sensor doesn't quite match the specifications. It follows the same constant pattern of the more vacuum the less voltage but the idle voltage starts higher at around 4.8V before dropping down to almost zero.

The MAP sensor reads the vacuum or negative pressure.

The MAP sensor works measuring the pressure in the intake manifold it does using a membrane to seal the reference chamber, as the pressure increases the membrane deforms and produces a voltage. The higher the pressure in the manifold the more the membrane will deform more and therefore the higher the output voltage.