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Is that clearing worth mapping?

Stochastic screening

Translating symbol size to ground size and vice versa

This is the first of occasional tips aimed at less experienced mappers. They can be selected via the 101 (as in course 101) tag.

Not infrequently I think a small clearing might be worth putting on the map only to find that it is microscopic when I add it. Sure, if it is very important to navigation, I can exaggerate it on the map but that is rarely the case.

Another frequent poser occurs when mapping a track. Is a noticeable but shortish section of change in rideability feasible to show?

I realised I would save a lot of time if I knew while in the field whether these and similar features would be distinguishable on the map.

Translation table

This table can be translated both ways. Although it is for foot orienteering maps, the principles can be used to prepare for other situations and indeed for other scales of orienteering map. The image below is low resolution (click on it for a larger image) but download links for high quality PDF and OCAD files are also given below.

When you see that the symbol for a small boulder translates to 6m spread on the ground, you quickly realise why boulder cluster and boulder field symbols are necessary. This situation also reinforces why the relationship between features is important as we  cannot always plot them precisely on the map.

ISOM 2000 symbol to terra firma sizing

If the person who created this guide back in 2001 contacts me, I will be pleased to acknowledge their work.


[ilink url=”” style=”download”]ISOM symbols sized on the ground[/ilink] This pdf is at 1:7,500 for ease of reading.

[ilink url=”” style=”download”]ISOM symbols sized on ground – OCAD 9[/ilink]  This is a zipped file. OCAD v9 format offers widest compatibility.

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