Discussion: Centre of the control circle where should it be?

The question arose should the centre of the control circle be situated directly over the location of the flag or should it be centred over the encircled feature with a description on the clue sheet saying where the flag is relative to the feature.

Can anyone confirm where it should be?

Point features: Centered on mapped feature
Area Features: Centered on location of flag

So is a point feature anything that will fit in the control circle e.g. a small cliff? So the circle could be encircling the cliff yet the clue sheet indicate that the flag is at the south end of the cliff?

A cliff is a linear feature.

Prepares for flames.

702 Control Point
The control points are shown with circles. The centre of the circle shows the precise position of the feature.

The definitive source for answering this question, with examples to match almost any situation:

http://orienteering.org/wp-content/uploads/2010/12...

No disagreement with the main principle (point/ line feature), but when there are many small features (similar or dissimilar) within the circle, I have observed that offsetting the circle on a small line or area/contour features can create confusion as to which feature the control is on. I don't think the rules and examples adequately address this.

I'll suggest he first job of the circle must be be to highlight the actual control feature. Further describing the actual location is a considerate, but secondary role. Furthermore this is a redundant role since the control description already provides this information.

So how large does a small line or area/contour feature need to be to warrant precise offsetting of the circle? I don't have a completely quantifiable answer, but I think all area/line /contour features drawn to the min. permitted size should be treated as point features. Other than that, I believe that simple use of eyeballs and common sense, on case by case basis will provide reasonable solutions.

I agree with EricW 100%---eyeballs and common sense.

One situation possibly in need of further discussion is sprint maps. It's the opposite situation of Eric's "minimum permitted size"---The features are so big, it's almost silly to center the circle on the feature and force the runner to use the clue sheet.

Full disclosure: For both sprint and normal maps, I am probably 95% compliant with my own advice (2nd post). For example, one place I fudge the circle is on the end of a linear feature such as a dry ditch or gully. In Condes, I'm zoomed in so much the circle is at least golf-ball-sized, and I'm placing the crosshairs very precisely. When I put the crosshairs on the last dot of a dry ditch, for example, and then print the map and look at it, sometimes it's like an optical illusion---it just looks wrong. On the very big features on a sprint map, I tend to center the crosshairs on point features, but that is where I get the most comments and questions. On sprint maps especially, there is the opportunity to "suggest" the offset in a very subtle way such that the feature is still very obvious (and usually no one comments about it).

There is nothing in IOF Competition Rules about where to draw the circle on the map, but the mapping specification ISOM covers it, as quoted by walk. This would seem to me to imply that any offset for a point symbol should be minimal, if at all. For a small line feature such as a short cliff, where the control is placed at one end, the circle should be offset. However, where the smallest possible cliff symbol (length 0.6mm at 1:15000) has been used to draw the cliff such offset is going to be so small as not to be noticeable.

Can I suggest to EricW that the presence of many small similar features within the circle might be a signal to find a different control site?

At sprint events a control might be on one side of an impassable fence or wall - it is appropriate I think to offset the circle to clearly show which side so as not to trap competitors.

Remember that a boulder is drawn as something like 8m in diameter, so the north side of a 1m boulder is still well inside the dot.

@Neil -- thanks for clarifying, now this whole thread makes much more sense.

"...where the smallest possible cliff symbol (length 0.6mm at 1:15000) has been used to draw the cliff such offset is going to be so small as not to be noticeable."

Absolutely disagree, and this is one of the most common examples. This is especially problematic in situations involving dissimilar, often overlapping, point/line/area/contour features.

In the above-sited IOF document, check out the example for "upper cliff". Is this circle correctly centered?


"... the presence of many small similar features within the circle might be a signal to find a different control site?"

Completely seperate issue, and a likely thread hijack. (proabably agree in many cases involving identical features, but disagree in cases involving only similar features or dissimilar features.)


"At sprint events a control might be on one side of an impassable fence or wall - it is appropriate I think to offset the circle to clearly show which side so as not to trap competitors."

Agree, a nice touch.

Simmo likes trapping competitors on the wrong side of closed gates that are mapped as open.

Thanks, glad to see the debate!,

The international specifications for control specifications 2004 link shows the answer . As best as I can see it puts the centre of the control circle directly over the flagged location.

Neither the ISOM nor the 2004 Control Descriptions document addresses this perfectly.

As walk has written, " The centre of the circle shows the precise position of the feature."

But the 2004 document defines the feature as column D, or some combination of columns D-F. Column G is specifically not the feature, but the placement around it.

That's good enough for point features (which until now I considered as symbols that are point features in OCAD, such as boulder, pit, small ruin, etc), but it would prevent me from using something like "(large) clearing, north part", which I do all the time. It seems like for certain linear and area features, the "feature" is column D-G.

I use "clearing, north part" in bad visibility, when "clearing, north edge" is too hidden.

A problem with that document is that it predates ISSOM. Those rules self-evidently weren't written with Sprint maps in mind. Like many rules, they aren't ideal when applied inflexibly to cases which the drafters hadn't thought about.

(but that's enough about the US Constitution ... )