Contour zones are designed into a mattress to help keep your spine in neutral alignment, allowing for more sinkage or more support in the required places.
Usually, a zoned mattress has three, five, seven, or nine contour zones, divided in the following manner:
Pelvis/hip: This part of your body is generally the heaviest and requires the most support if you’re sleeping level or the most sinkage if you’re sleeping on your side.
Lordosis/lower back: This point usually needs to be extra firm to prevent the formation of a hollow back.
Shoulders: Like the pelvis/hips, the shoulders need more support or more sinkage, depending on your sleeping position.
Head/feet: The head and feet are generally light and need to lie flat on the mattress.