Caleb Gould (GBR)

There is a range of different problems which can be set by Trail-O planners in their selection of control sites and the placing of flags to give Elite Trail-O competitors the necessary variety and technical level of challenge.

This paper attempts to identify and categorise the different types of problem which can be constructed for elite competition. At elite level, control sites usually present a combination of types of problem.

All the examples listed here are from the two days of the World Cup Trail-O held in conjunction with this clinic.

Skills expected of competitors

  1. Terrain recognition is the prime skill required at elite level, plus the ability to match the terrain precisely to the map, allowing for any omissions due to generalisation.
  2. Distance estimation to 25%.
    i.e. flag at 40m; estimate in range 30 - 50m
        flag at 100m; estimate in range 75 - 125m
  3. Bearing measurement, using standard competition compass, to 5º.
    Problems should not be set where the use of a precision compass would give an advantage.


Which Feature?

This is the selection of a number of similar features on the map in a small area. The problem is to identify which feature is the correct one using a choice of techniques, including the description.
Example: D1/ET - NE Rock face. All five flags are at the foot of rock faces but the largest, on the map and in the terrain, allows the correct feature to be readily identified.

Which Edge?

A common problem is a single large feature, such as a marsh, and the competitor has to decide which edge is the correct one. The problem can be solved by careful attention to the circle position, description, adjacent features, bearings, etc.
Example: D2/ET - Marsh, SW edge.

An adaptation of this is to have no flag on the correct part which makes the problem a little harder, as the competitor tends to look for a correctly positioned flag before thinking that none of them may be right.
Example: D1/E10 - Boulder Field, SW edge.

Which Part ?

Simple terrain recognition, involving the choice of a number of parts of a feature. Normally may be another feature to key in the problem. This may involve careful reading of the description, see under 'Precision of description'.
Example: D1/E4 Depression, South edge.


Indistinct boundaries

This involves the edges or ends of features which are distinct on the map but much less so on the ground. Examples include the edges of marshes and the ends of tapering ditches and gullies.

Use of such features is possible if there are adjacent features which allow the position of the flag to be adequately judged.
Example: D1/E11 - Marsh, West edge. The correct flag is on an indistinct edge but the other four flags, three on distinct marsh edges and the fourth on the edge of the clearing, locate it precisely.

Subtle Shapes

These are sites where the ground shapes are less obvious on the ground than the contours which portray them on the map. Recognition of such ground detail may require some attention.
Example: D2/E2 - Spur, SW side. The spur form line on the map is a weak feature on the ground but the clump of trees identifies its position.

Complex Ground Shapes

Terrain recognition to a high level is required, with the competitor needing to analyse a complex area of ground shapes without the use of outside fixing features.
Example: D1/E5 - Southern Spur, an area of many spurs and re-entrants.

Floating viewing point

In these cases the position of the viewing point cannot be fixed and, in turn, cannot be used for fixing positions of the flags. These have to be deduced from inspecting the relationships between the features in the terrain.
Example: D1/E12 - Hill, East side. The viewing point is on the track with nothing to fix its position, other than the flags in the terrain.

Right Feature - Wrong Position, Wrong Feature - Right Position

This is a situation where there are two parallel similar features. Flags are placed on the correct feature but not in the position indicated by the description. On the parallel feature one flag will agree with the description, but it is the wrong feature. Therefore the answer will be that none are correct.
Example: D2/E3 - Hill, SE side. The correct hill has flags on the W and S sides; the second hill to the East has a flag on the SE side.

Ground Height

The ground height and shape can be deduced from the visible height of the flags (provided the Planner takes care to ensure that all flags are installed at a standard height).
Example: D2/E15 - Hill, SE part. The distinction between hill top and hill part or hill side is deduced from the apparent height of the flag. In this case the flag is just visible above the top of the hill and is clearly positioned beyond and below the top.


Back Marker

This is when the key to the problem is a feature behind the competitor, for example on the other side of the viewing track. This can be used in different ways:


This is the extension of a linear feature, typically from the far side of the viewing track, to fix the position of the required flag.
Example: D1/E8 - Spur. The extrapolation of the vegetation boundary through the centre of the control circle allows the same to be done on the ground and thus indicate the correct flag of the five on this featureless ridge.

Secondary Viewing Position

A secondary viewing position gives a clear indication of the correct flag. The competitor then has to move (back) to the viewing point to select the letter for this flag.
Examples: D1/E3 - Vegetation boundary. From the viewing point all four flags appear to be on the edge of the thicket. Viewing from a position level with the flags shows that two of them are on isolated trees well away from the vegetation boundary.
D2/E13 - Re-entrant. The correct flag can be easily identified by viewing down the small re-entrant south of the viewing point.


Ghost Features

Similar features to that indicated by the control circle appear to be present on the ground but are correctly not shown or shown differently on the map. These 'ghost' features are flagged and the competitor's task is to distinguish between them and the mapped feature.
Examples: D2/E4 - Hill top. The flags on the ridge and spur appear to mark hill tops, as they appear from the viewing point.
D2/E6 - Hill, East side. All five flags appear to be marking the east side of hills, three of which are small and unmapped. Ignoring these and concentrating on the larger mapped features yields the correct answer.

Wrong Feature

All flags are on a nearby similar feature but, if the viewing point position is reasonably carefully determined, this wrong feature becomes clear and the zero answer is obtained.
Example: D2/E8 - Spur top. All flags are on the parallel spur to the north.

Precision of Description

This is the case where there are many flags close together and the key to the problem lies with careful reading of the description sheet. In such cases it is not possible to directly determine the answer from the map and bearings alone.
Example: D1/E13 - Middle Spur, West foot. The description is needed to distinguish between spur top and foot, as well as which foot.

Overlapping Sites

This is where two or more control sites use one cluster of flags. It is good practice for not all of the flags to be visible from each of the viewing points; the disappearance of flags and fresh ones appearing as the competitor moves from one viewing point to the next add interest.
Example: D1/E1&E2 Spur, top and Hill, NE side. Six flags are used, with five flags visible from each viewing point.


This occurs when the flags change their left-to-right identifications when viewed from different positions.
Example: D2/E11 - Ditch Junction. From the viewing point the ditch junction cannot be seen but it is clearly visible from a position several metres further along the track. But the letter code for the correct flag is very different at this secondary viewing point compared with that for the marked viewing point.



Several flags appear to fit the control description. Use of the compass eliminates one or more, to leave the required flag by itself or in a group from which it is identified using other techniques.
Example: D1/E7 - Western Vegetation boundary. All four flags appear to be on vegetation boundaries, one of which is indistinct and unmapped. Use of the compass narrows the choice to two which are then separated by reference to nearby features.


More than one flag fitting the control description lies within the 5 degree arc of bearing accuracy but they are at different distances. Provided the separation in distance between the correct flag and the nearest alternative is 25% or more, the correct answer is achieved.
Example: D2/E5 - N Re-entrant. Identification of the northern re-entrant reduces the options to two flags, but that at the head of the re-entrant is too far away.


For timed controls the problem needs to be clear and not require the competitor to move around to establish the answer. It must be remembered that competitors only have one minute to choose which flag marks the correct position.

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