I have been doing some reading/video watching on cell shading after this was recommended to me by Gary. It is actually fairly simple once you get started; it just involves using several fill shaders in Maya, from the 'Toon' Menu
The sun and sky in this are just simple Solid Colour textures, whereas the trees and terrain are Two Tone and Three Tone Shaded Brightness textures; which have had a Ramp shader applied. I simply created the sense of lighting as the sun rises by keyframing the ramp shader, so the ratio of black to brown/white eventually decreases. Although, I know that the timing is a bit off in this video.