AHP is to model the problem as a hierarchy. In doing this,
the aspects of the problem at levels from general to detailed
were explored, which can help to increase the understanding
of the problem, of its context, and of each other’s thoughts and
feelings about both. Then it was expressed in the multileveled
way that the AHP requires. The hierarchy consists of an
overall goal, a group of options or alternatives for reaching
the goal, and a group of factors or criteria that relate the
alternatives to the goal. The criteria can be further broken
down into subcriteria, sub-subcriteria, and so on, in as many
levels as the problem requires. Similarly, the hierarchy of the
impedance factors for emergency routing in GIS was firstly
established. According to the logical relationship between
impedance factors, the hierarchy was created as the following
Fig. 1.