You need to identify your periods of interest first, bearing in mind the challenges and limitations of each sensor used in the epochs you identify.

You should then harmonize the various images (pre-processing) so that you can use them seamlessly

Decide on the mode of classification to use (supervised vis unsupervised; hard vis soft etc)

Perform your classification

Validate your classified results (ground truth data)

Perform image dfferencing ... to obtain insight into how the urban growth (sprawl) has occurred.

You can then do your projections of future growth based on some of the models in existence.

I do hope you have an easy time with your research ... and avoid some of the pitfalls many of us had to endure.

thank you very much , i already downloaded some lansat etm+ , tm, mss for 1970 1990 2000 2006 , different sensors , i dont know if the pre-processing is the same , trying to get a document (step by step) from the pre-processing ,classificaion and for the simulation( planning to use IDRISSI soft). i am a bit familiar with envi and argis

i have one year o get it done ,hope to defend in june 2011 , not easy for the first time working on this

thanks again