GIS serves as a means to catalog both the behaviors of the natural world and the built world, and the interaction between the two. Risk is inherently a spatial phenomenon, and can be assessed with a good degree of certainty if reliable spatial data has been collected over time. Knowing the behavior of a locality in the face of past events of different intensities provides a reliable indication of how systems and structures will react to a hypothetical or real-world event.
Different types of spatial data are needed in order to assess the risk of different hazards. Flood modeling requires topology data and an understanding of the behaviors of interconnected watersheds. Assessing seismic hazards and landslides requires modeling of subsurface geology, seismic faults, terrain, soil structure, and vegetation. Assessing the impacts of natural disasters on populations requires a mapping of infrastructure, population densities, land use patterns, and a fine-grained analysis at the intersections where the highest risk to humans is likely to occur.
The patterns and intersections of hazards and risks to both human and ecological health are staggeringly complex as a whole. Our ability to measure and respond to such impacts lie beyond the understanding of individuals, because we have a very hard time comprehending how small failures can lead to catastrophic consequences.
GIS is an extremely valuable tool for estimates of hazard-related damage before or after a disaster occurs, particularly when combined with sensors to inform our models. Through GIS analysis, estimates can be created for physical damage to infrastructure, economic loss to do interruptions of commerce, and the social impacts to populations that may now lack homes. Used by both government and business, these tools and models can be used to take preventive actions in order to drive down the costs of inevitable natural events.