Nominal. It includes only names, which are the result of a classification.These names are not ordered in a specific way: rather ther thay describe different categories of the same rank. So, the only conclusion to be made is the inequality of each class. Transportation infrastructures are particularly suitable for nominal representations. Networks and terminals can be classified by function or ownership. On figure 4.12 this involves a simple distinction between Interstate highways that are toll and those that are regular (non-toll). There is no order in this classification since each class is simply different from the other.