In the threshold determination phase each vector component j of each map
unit i is assigned a threshold value 
.
All thresholds are determined automatically by the following procedure.
Figure 2: The Voronoi set 
of the map unit i
(in a two-dimensional case).
For each map unit i the set is defined to include
only those input vectors 
for which the unit i is
the best-matching unit, i.e, the set consists of those input
vectors which belong to the Voronoi set of the unit i
(Figure 2),
where 
is a weight vector of the map unit k.
If a uniform distribution is assumed for 
, the jth component of
, the mean of the is given by
The confidence interval for is now defined as
where 
, and d is the confidence level.
We can now define the thresholds as
