Silhouette Plot - Vertical Axis

Hi,

How does silhouette(data, labels) function plots silhouettes? The vertical axis is named as 'Clusters', but Ylim function returns a number that is so larger than the number of clusters; as an example, bigger than 5 millions for 5000 clusters. Why is that?

The graph for 5000 clusters gives no information, but for 20 clusters it is very informative. I tried to see only a small portion of the 5000 clusters using axis([-1 1 Ymin Ymax]) command, but it did not help, and while trying to do this, I figured out that I did not know why there are many more points in the vertical axis than the actual number of clusters.

Silhouette values are calculated for each point (observation) in the data. How is the plot created using these values?

Thanks in advance.