2.5D ("two-and-a-half-dimensional"), 3/4 perspective and pseudo-3D are terms used to describe either:

• graphical projections and techniques which cause a series of images or scenes to fake or appear to be three-dimensional (3D) when in fact they are not, or
• gameplay in an otherwise three-dimensional video game that is restricted to a two-dimensional plane.

(Information taken from Wikipedia.org)

I have a question based on 2.5D game development. As stated before, 2.5D uses graphical projections and techniques to make fake 3d or a gameplay restricted to a two-dimensional plane.

A good example is a TQ Digital made game: Zero Online (screenshot) the whole map is made of 2d images and only NPCs and players are 3d.

The maps were drawn manually by hand without any 3d software rendering. As I'm playing the game I feel like I'm going from a lower part of the map (ground) to a higher one (some metal platform) and it feels like I'm moving in 3 dimensions. But when I look closely, I see that the player size didn't change and the shadow too but I'm still feeling like I'm somehow higher then before (I had rendered a simple map myself that I made in 3dmax but it didn't quite give the result I wanted).

How to accomplish such an effect?