Ok, might seem obvious, but I'm just curious: what defines an estate car? (I drive a mazda 323 lx hatchback, which is much longer than other hatchbacks, but would hardly be classed as an estate)
A hatchback is much like a standard saloon body but with the rearwindow/boot section combined into an inclined hatch to access the cargo area.
In an estate car the roof behind the rear passengers is extended backwards, giving the cargo area "full height" until it reaches a more vertical access at the back.