There are two main paradigms in the urban hierarchy:
- Christaller Model. According to this model, a dominance
relationship is established between several orders of the hierarchy.
This relationship implies that a center of a lower order must rely
on a center of higher order for goods and services not being supplied.
- Pred Model. Christaller's model was adapted by Pred in
order to confer more flexibility. The hierarchical structure becomes
less rigid, but more complex. The first point worth mentioning is
that centers of the same order are not necessarily at the same hierarchical
level. This shows that some centers offer more diversified goods
and services than other centers, even if they are of the same size.
Interdependency implies that central places can exchange
similar goods and services. Complementarity enables several
centers of a similar order to specialize in specific activities
and supply themselves in goods and services they do not have from
other centers. This implies the notion of economies of scale reinforcing