Where the second dimension tells something about the memory size and attributes correlating with that, the first dimension seems to separate older from newer products. This can, for instance, be seen in Figure 17.11, where we labeled products by the Interface attributes. Since Interface is a multi-valued categorical attribute, we have chosen to label each product only by a single value, namely the one most frequent in the product catalog. Also, we only show the category points of the three most occurring categories, since all products belong to at least one of them. As said, there seem to be two groups, the older MP3 players supporting USB and the newer ones supporting USB 2.0. For the operating systems attribute one can observe a similar pattern.
More generally, the NL-PCA approach creates a map in which more of the available space is used than in the MDS approach. However, most of the map is used to visualize the special, not that common products, while the ordinary products are cluttered together near the right top corner of the map. Also, the map only shows those products and attributes that do not have too many missing values.