As an example, a flood is a natural hazard; flood risk is defined in terms of the hundred-year flood; the people and buildings located within the hundred-year flood zone are vulnerable, and a flood disaster is a flood that injures a number of people, or causes significant damage.Alexander (1993) has taken a relatively formal approach to this process by using conceptual equations, a system that lends itself well to the perspective of a GIS research community who often strive to formalise (see Johnston, Chapter 3)