I wont be able to give a great deal of information on this, but there are certain rules I think we need to follow for training sites:

• Training sites should be spread all over the image i.e. should be covering a large area and not just focussed in a region
• Just as Georeferencing, training sites should be identified at the corners and at points which give maximum sampling options
• The objective is to identify a set of pixels that accurately represents spectral variation present within each information region

Hope it helps...

I wont be able to give a great deal of information on this, but there are certain rules I think we need to follow for training sites:

• Training sites should be spread all over the image i.e. should be covering a large area and not just focussed in a region
• Just as Georeferencing, training sites should be identified at the corners and at points which give maximum sampling options
• The objective is to identify a set of pixels that accurately represents spectral variation present within each information region