- Category: Segmenting the Map
- Published on Friday, 28 September 2012 02:46
- Hits: 10377
Segmenting the map for a search is best understood in the context of a search. As an example, we will look at a fictitious search for a lost child. In this example we use the bicycle wheel model.
We will imagine that an 11 year old boy, John Doe, is missing and was last seen at the day use parking area shown on the map below. For reference, the 25% region from Koester's book is marked on the map as a red circle around our Initial Planning Point (IPP), which also happens to be our current PLS.
Examining the area with a variety of maps, we see that the network of roads around the IPP comprise a campground. Travel is easy in the campground, so we will include it in our first search area, in addition to the trail head across the highway. This hub is 45.6 acres and will require several field teams to search in a timely manner.
There are several trails and roads leading away from the hub of our preliminary search area. These will become the spokes of our wheel, but first we must make an estimate of how far out to go. In this case, we have chosen a 1 mile radius from the IPP. This measurement was obtained from Koester's book as the 50% zone for children of this particular age.
The likely paths leading away from our IPP are the spokes. In this case, we have several trails and roads on the map. Since this is a fire prone area, no single map or satellite image is guaranteed to provide an accurate picture of the paths on the ground, so a variety of sources are required to come up with these segments. There are often other areas of interest we want to search, such as the summit to the east of the IPP. These are sometimes referred to as the reflectors of the bike wheel.
Our initial search segment, the hub, was large enough to occupy several field teams for an hour or more. If the subject were not found in that initial effort, the step of expanding to the 50% region, 1 mile in radius, would have given us a search area of just over 2,000 acres. The 11 search segments comprising the spokes and reflectors of our bicycle wheel model totaled 270 acres. For reference, creating these maps and writing this article took about 1.5 hours. This is probably similar to the amount of time required for someone in the plans section to write assignments and produce maps for 11 field teams.