GRASS and river classification

[N R A]

Can anyone provide any information on this problem.

Our organisation carrys out an annual classification of the English & 
Welsh rivers. This ranges from 1A (excellent) to 4 (poor). We can produce 
maps that show the various stretchs of the rivers coloured according to 
classification on our old mainframe system - it uses a series of 
classification points which have a certain class and apply upstream along 
the river until another class point is found.

I'd like to use GRASS to create these maps - the question is how ??

We have the rivers as a vector dataset and I've loaded and plotted these. 
How can I get different parts plotted in a colour corresponding to the 
value of a point or do I have to somehow create a vector set for each 
year of classification - but this would involve storing the coordinates 
many times.

Thanks in advance for any help, 

Steve Culshaw
NRA North West
e-mail : nra at cix.compulink.co.uk (use this for general usage)
or         sculshaw at cix.compulink.co.uk (Private - only checked at best 
biweekly)