The three zones in handwriting are based on the freudian model (id, ego and superego). The three zones are: lower (id), middle (ego) and upper (super ego).
Here is a quick, high quality picture I have whipped up in paint to give you a quick idea of what zones are:
Graphology Zones in Terms of Time:
The Lower Zone is the past
The Middle Zone is the present
The Uppser Zone is the future
What Do The Three Zones Mean?
Nice question - here is what you can analyse from the three zones.
Firstly, the zones can be interpreted just like a human body with the head being the mind and what we think. The middle being the heart, feelings and body - thus representing everyday life. The lower zone referring to the lower body - urges, sex and desires.
What each zone resembles:
Lower: Money, health, sex, home life, physical urges and desires.
Middle: Also known as the ego - whether the person is happy with their life. How they feel of themselves compared to other people.
Upper: The mind. Ideas, imagination, what you think and fantasies.
Next post will be about dominating lower, middle and upper zones, so stay tuned!