Janet Baraclough wrote:
The message
from asvensso contains these words:

Does anyone know if
there are any compelling reasons why the garden is laid out this way?

How could we?

. Ask your surveyor (local ones, are often a mine of local knowledge).
Or try the planning dept/council offices.

Possible reasons are, that the raised section contains runs over
buried tunnels, or drains /services to/from other houses/the street.
Take a look at the neighbouring properties; to see if their land is
at the same level. If yours was lowered, you might have to
shore up the neighbous' level or boundary walls/fences.

Janet

IME soil gets moved about because it costs a lot to get rid of it