I have a polygon shapefile which has population attributes pop90,pop91 and so on for 10 years. They have different minimum and maximum value for each of the years. Now I need to do classification for each attribute(pop90,pop91) but with the same number of classes and the range for each class should be same. Same number of classes is fine but I am not sure on how can I use the same class range for each of the attribute. Any idea how can this be done. Thank You.