A powder blast zone is also defined in areas where it is applicable. The accuracy level of these maps correspond to the maximum possible level of accuracy obtainable from detailed analysis of a large avalanche path. Such detailed maps are rarely available in the United States. They do not provide sufficient detail for site-specific planning. Detailed avalanche hazards maps are sometimes shown on high quality air photographs, usually at a scale of 1 - 10000 or larger.
Photographs have some advantages over maps in that they show trees, boulders, and recent buildings.
These provide good reference points for hazard lines. Because of the lack of detailed maps in the United States it is required that careful field study be made of the starting zones, tracks and runout zones for all detailed avalanche studies. Even after detailed studies have been completed there still exists some uncertainty about the limits and dynamics of the avalanche which must be planned for. More generalized avalanche planning maps have been prepared for selected areas in Colorado by several sources. One set of maps were prepared by the Colorado Geological Survey.