Figure 2.23 An Example of an Overlay Map Used for Risk Assessment

Earthquakes

Figure 2.23 An Example of an Overlay Map Used for Risk Assessment

Source: Overlay maps completed by Pathways Group at Natural Resources Canada and presented as a contribution to the Canadian team in the “Bridging to the Future Project” (Sheltair Group 2007). Note: Combinations of landscape risks may be overlaid to create a map for multihazard risk assessment that quickly and easily communicates which landscapes are suitable for specifi c uses.

locations function as both supply and demand nodes for fl ows of resources.

Focus on quality inputs Similar to the case of meta diagrams, the diffi culty in overlay mapping is the scarcity of reliable data. Maps may be beautiful, but their utility depends on the accuracy and scope of the data that have been supplied. In fact, the mapping of ecological resources within and around a city, for example, is a relatively simple task that may be performed by any recent college graduate. However, inventorying resources is not so simple. A substantial investment is sometimes required to survey resources and document conditions throughout a region. The process involves experts in many disciplines. Because every location is unique, there are few shortcuts. One technique for speedy data collection is the use of photography from the air, in combination with a global positioning system, to create data rapidly on the length and area of the natural and built elements of a region, including building footprints, the length of key streets and shorelines, and the characteristics of open