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Before any search can commence the search manager must define a search area. This will almost always be done in consultation with the management team/other search planners. This is a critical step in the preparation of a search plan, the strategy and tactics of any search operation.

To establish the search area known or presumed information must be applied to come to a logical conclusion about the boundaries of a search area.

These boundaries are basically lines drawn around an area of a map. As the search commences and progresses the search area may have to be expanded and more sharply defined as more information becomes available.

The base point from which to plot the initial distances or draw the initial boundaries is the IPP, which as we know, can be either the point last seen (PLS) or the last known position (LKP). The IPP never changes but the PLS or LKP may as the search and investigation progress.

The search area is the total area to be searched. The boundaries of the search area can be defined by:

The area outside of the actual search area is known as the Rest of the World – ROW. There is always a chance the subject is not in the search area and expansion into ROW can occur if:

Four Methods of Establishing the Search Area

1.         Theoretical – This is the distance the subject could have travelled in the time since becoming lost.

2.         Statistical – This is the information available from past cases in the lost person behaviour databases.

3.         Subjective – Evaluation by the search manager of factors such as natural barriers and terrain features to clues left by the subject.

4.         Deductive Reasoning – Methodical analysis of the circumstances looking at all the facts and circumstantial evidence and logically deducing where the subject may have gone.

Theoretical

This is a plotted line on a map showing the distance the subject could have travelled from the LKP/PLS. In theory the subject could travel in any direction from the IPP.

The search manager should consider the total area (i.e. of a circle in which subject may be). This can be illustrated as follows:

Theoretical Search Area = Лr² where Л = 3.14

Example:

Subject travels 1 mile,    search area is 3.14 x 1² = 3.14 sq. miles.

Subject travels 2 miles   search area is 3.14 x 2² = 12.6 sq. miles.

Subject travels 3 miles   search area is 3.14 x 3² = 28.3 sq. miles.

The importance of early confinement of the subject to limit distance travelled is evident. However, whilst we must consider theoretical distances we generally use the statistical databases to identify the:

Statistical Search Area

These are the statistics from previous incidents. Remember they are planning tools, not absolutes.

With these statistics we can plot/establish zones of probability. For the moment we can view these simply as circles on the map only. The search area within these circles will be further defined by the application of:

Subjective Reasoning

This includes limiting factors such as natural barriers (rivers, cliff faces etc ) where we can reasonably assume, for the time being, that the subject hasn’t managed to overcome or pass.

The search area circle will be more clearly defined by the application of other historical data from past case histories (the databases), for example the figures which may show a certain category of subject more likely to go downhill than uphill.

We can also consider the physical and mental limitations of the subject. For example, a 90 year old subject who has a severe walking disability and who has left his home without his walking sticks. He clearly wouldn’t have travelled too far.

Also consider likely spots such as:

Once the search manager has established the search area, taking all factors into account then the search area must be ‘broken’ up into manageable sizes:

Defining Sector/Segment Boundaries

We have to break the search area up into smaller sectors in order to divide the total search area into more manageable units which can be controlled by the search manager and which can be searched more efficiently by the search teams.

The actual sectors themselves can be defined by any number if factors which can be easily recognised and identified by all searchers, such as:

1.         Man made – Fences, roads, power lines, paths, railway lines, field edges, walls etc.

2.         Natural – Streams, rivers, ridge lines, and vegetation breaks etc.

3.         Improvised – Line of sight between 2 features, flagged/stringed straight lines.

In some flat areas with few features it may be necessary to create lines such as stringed/flagged lines, usually on a compass bearing. A bearing in itself is of little use.

Where boundaries are unavoidably vague some overlap is more desirable then the chance of missing areas.

Sector Sizes

The type of terrain is a major factor but whatever size is chosen it should be such that it is capable of being searched by a search team in 4-6 hours or half a shift. This allows the team to complete one task, have a rest break and then continue. This is good for the search team as they will have a sense of achieving their objective.

Large segments             Bad for morale

                                    Difficult to cover in given time

                                    Difficult to ‘pass on’ to next shift

                                    Causes delay

Small segments             These cause logistical problems due to the search team having to move too often.

Make the Search Easier for the Searchers

Identification of Sectors/Segments

As sectors are drawn on a map they need to be numbered or lettered. This makes identification, planning and communications easier. If necessary sectors can be sub-divided and sub- lettered.

Copies of the sectored maps should be given to all search team leaders to assist with re-deployments.

At the ICP the master map should be covered with a transparent overlay onto which all relevant information can be recorded as the search progresses.

Prioritising Search Areas

This should be done by the planning team in a consensus, similar to that already done for the scenario considerations.

Each planner should complete a worksheet as follows, using values 1 – 9 as before, 9 being the most likely. The sheet could hold 10-15 sectors.

9 -        Most likely

8 -

7 -        Likely

6 -

5 -        Even chance

4 -

3 -        Unlikely

2 -

1 -        Least likely

Consensus Worksheet 1

To be used by each evaluator

1. Place evaluator name on sheet and assign an appropriate likelihood number to each sector (1-9)

2. When filled out, each evaluator’s worksheet will be combined into a group consensus worksheet #2.

Once each individual planner has completed their own worksheet they should be included on a collective weighting worksheet:

CONSENSUS WORKSHEET 2

1. Insert evaluator names in left column

2. Carefully record each evaluator’s likelihood values for each sector. There is room on this sheet for up to 6 sectors (A – F). There may be up to 15.

3. Add each sector column and put this sum in the ‘subtotal down’ space at the bottom of each column.

4 .Add the totals for all of the columns. This value now becomes the denominator for the fraction that will be used to determine the sector weight.

5. Calculate sector weights by dividing each ‘subtotal down’ figure under each sector column by the total of all sector weights. (Subtotal down divided by total of all evaluator weights =weight for each sector, expressed as a %)

The worksheet would normally contain 10-15 sectors. The above is for illustration purposes only.

Now that all aspects of establishing the search area have been discussed the methods can be reinforced and illustrated with reference to the following topographical maps, marked in stages.

This is just the basic map of a typical search scenario. Without getting into specifics and using any category as an example, assume the lost person was last seen on the ridge line in the centre of the map to the west of the large lake.

At this stage you would have identified the category of person sought and have access to the behavioural characteristics and databases of past cases.

MAP 1

Here, the IPP has been marked towards the centre of the map.

Then, for illustrative purposes only, the 25% probability zone, median distance and 75% probability zone have been superimposed on the map.

It is up to the search manager which zones are used. Many prefer to put the median distance and maximum zone. Others prefer to make the outer circle the 75% zone as the maximum can sometimes be too large for the map in use.

The next stage would be to outline the statistical search area whilst taking into account certain geographical limitations to the search area.

MAP 2

Here, the basic search area has been outlined. The boundary to the west goes along a number of ridges and to the east along the river bank and lake edge.

To the south there is a defined river bank but still the possibility the subject may have gone around to the south of this river from the westerly direction, hence another apparent area.

The next stage is to apply some more statistics and reasoning to the search area according to the specific database being referred to and with reference to the geography involved.

MAP 3

For the purpose of illustration only, the subject is believed to have headed downhill along the path of least resistance, towards the lake as the subject has a particular interest in water and wildlife. However, analysis of the map shows a small lake to the south east of the IPP so this would be included in the more focused search area.

Again, we would have to bear in mind the limiting features of the geography and we may be able to make certain assumptions such as the subject could get to the rivers edge or lakeside but couldn’t actually cross it.

The next step is to break the search area into more manageable sectors/segments.

MAP 4

The search planners have by this point looked at the map, analysed the information and divided the search area into search sectors.

The previously shaded areas on map 3 have been allocated the highest priority and the rest of the search area lower down the scale.

Sectors can be given numbers or letters. Many prefer letters to avoid confusion, but it matters not as long as the maps are clear.

Again, for the sake of the example, there is no right or wrong answer to this sectorisation. When applying the theory in a real situation the search planners will have had full access to all information and agreed between themselves the search area and priorities.

Applying Mathematical Values

For those interested in number crunching, there is now the possibility of assigning POA’s, POD’s and therefore POS’s to each of these sectors.

The benefits of doing this have already been explained in some detail, but hopefully the methods shown for prioritising sectors, having identified the search area will still provide the correct direction/reasoning for the search, albeit without the specific mathematical calculations.

The subject of assigning mathematical values is itself a lengthy one and not within the remit of this handbook.

If it is thought these are absolutely necessary the search manager must consult a suitably trained and experienced person. This would be a person fully trained in lost person search management, but as the MRC statistics show most searches do not go beyond 12 hours.

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This site, whilst created from the perspective of a police officer, is a personal work. It does not necessarily represent the views or policy of Devon and Cornwall Constabulary.

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