How do you know which is the closest class example(observation) to a class in Self Organizing Map?

Question

For example there are two classes C1 and C2, distance1 and distance2,

The rule tells which class is: If distance1 > distance2 than class C1 (Node1) else class C2 (Node2)

Here are some data examples:

distance1    distance2     class
5.315        3.111         C1
9.544        4.322         C1
4.178        5.122         C2  
3.118        1.899         C1
8.198        4.334         C1

How can I tell which class examples are the closest to C1 class? Should I rank distance1 by the longest distance or shortest distance? Any suggestions?