I am trying to make a landscape scene. I want the landscape to have 4 different images as textures. The images should change as the height increases. I was able to do this with 2 images but when I increase the images it goes wrong. Also I found examples on stack which were using color ramp. Also when I use a mapping node for my images, the result is having only one Image. I use cycles engine.
Use different ramps, each one with a different increasing range, to map the information from the $Z$ axis.
(The math node in this case is not doing anything, but can help you refine the placement and scale the coordinates for the z axis. The ramp node's range is confined to values from 0 to 1 so if your values exceed that range or are too small you might need to scale them)
Then, each one of the ramps can be used as controls a color mix between two different images, and then concatenated to mix new images in different heights of the mesh.