Define new symbol characteristics. SYMBOL statements are assigned to the values of CITY in alphabetical order. For example, the value Minn is assigned SYMBOL1. 
symbol1 color=green interpol=spline
        width=2 value=triangle
        height=3;
symbol2 color=blue interpol=spline
        width=2 value=circle
        height=3;
symbol3 color=red interpol=spline
        width=2 value=square
        height=3;