Beyond Mapping
Estimating Response Times for Backcountry Emergencies
GIS modeling can extend emergency-response planning “beyond the lines” of a fixed road network—an important spatial reasoning point for GIS’ers and non-GIS’ing resource managers alike.
any road location. Note that the on-road surface forms a rollercoaster shape with the lowest point at the headquarters (TT = 0 minutes away) and progressively increases to the farthest-away location (TT = 26.5 minutes). If there are two or more headquarters, there would be multiple “bottoms,” and the surface would form ridges at the equidistance locations in terms of travel time—each road location assigned a value indicating the time to reach it from the closest headquarters. The lower-right portion of Figure 1 shows the calibrations for on-road travel by truck and off-road travel by ATV, hiking as a function of terrain steepness, and
BEYONDMAPPING
ne of the most important geotechnology applications has been Enhanced 911 (E911) location technology that enables emergency services to receive the geographic position of a mobile phone. The geographic position is automatically geocoded to a street address, and routing software is used to identify an optimal path for emergency response. But what happens if the call that “I’ve fallen and can’t get up” comes from a backcountry location miles from a road? The closest road location “as the crow flies” rarely is the quickest route in mounBY JOSEPH BERRY tainous terrain. A continuous-space solution is a bit more complex than traditional network analysis, as the relative and absolute barriers for emergency response are scattered about the landscape. In addition, the intervening conditions affect modes of travel differently. For example, an emergency-response vehicle can move rapidly along backcountry roads, and allterrain vehicles (ATVs) can be employed off the roads. But ATVs can’t operate under extremely steep and rugged conditions, where hiking becomes necessary.
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Backcountry TT
The left side of Figure 1 illustrates the on-road portion of a travel-time (TT) surface from headquarters along secondary backcountry roads. The grid-based solution uses friction values for each grid cell in a manner analogous to road-segment vectors in network analysis. The difference being that each grid cell is calibrated for the time it takes to cross it (0.10 minutes in this simplified example). The result is an estimate of the travel time to reach
Joseph Berry is a principal in Berry & Associates, consultants in GIS technology. He can be reached via e-mail at jkberry@du.edu.
F igure 1. On-road emergency-response travel times are calculated for this example.
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