Debris-flow hazard map units from gridded probabilities

The common statistical practice of dividing a range of probabilities into equal probability intervals may not result in useful landslide-hazard map units for areas populated by equal-area cells, each of which has a unique probability. Most hazard map areas contain very large numbers of cells having low probability of failure, and as probability increases, the number of cells decreases in a non-linear fashion. Exploration of this distribution suggests that the spatial frequency of expected failures may be used to identify probability intervals that define map units. From a spatial database of gridded probabilities, map units that address the different objectives of land-use planners and emergency response officials can be defined.