I want to display on a scatter graph all of the schools in
the north of England. Each school has a unique reference number. Each school
will have a grade from 1 to 4. This grade is the outcome from their last inspection.

What I need to be able to do is display all of the schools
by their unique reference number and have them permanently on display, in grey
as background data. I then wish to be able to select any grade between 1 and 4
and have those schools display on top of the greyed out schools, in different
colours.

Can anyone tell me how I can make this happen please?

1. Thanks.