Flooded Forest

[Red Adder]

Here's a good one for the mappers. How would you map a forested area (with the trees still very much alive) which has been flooded by an extended lake (seeming a permanent feature). [Or mangrove swamp even ?]

[GML]

What's wrong with Marsh (310) or Uncrossable Marsh (309), with a white (or green) background?

Remember that you are mapping what the competitor will see on the run/what they need to know for route choice purposes. A competitor can't see how deep a wet marsh/pond/lake is, and so the map doesn't need to distinguish, other than to be clear about whether the feature is crossable or not.

If for some reason it really is necessary to distinguish this feature from, say, an uncrossable marsh, then I would consider creating a special non-standard symbol e.g. a blue and white version of 404 (rough open with scattered trees), but only if absolutely essential to differentiate from uncrossable marsh (i.e. there would also need to be at least one uncrossable marsh on the map).

Graham

[Scott]

Technically, you're only allowed to combine the uncrossable marsh screen (309) with rough open (403) or rough open with scattered trees (404). Practically, I wouldn't see a problem with combining it with white forest (405) - might be worth a note in the start lane (and final details, if appropriate) so competitors are aware of the unusual circumstances.

[greywolf]

How would you map a forested area (with the trees still very much alive) which has been flooded by an extended lake (seeming a permanent feature). [Or mangrove swamp even ?]

Like this?

marsh.jpg (21.46 KiB) Viewed 4367 times

just a sketch map at the moment...as the area is flooded by the sea (not mangroves, sadly) the extent and depth of the marshy area is seasonal on 3 separate timescales: annually, monthly and daily, which makes accurate mapping rather problematic....

Scott: white forest isn't a "screen" in the sense of the table of P4 of the ISOM spec, so there's no problem with combining uncrossable marsh & white forest

[edit: alt answer: purple overprint for safety / environmental reasons]

[GML]

I think you are allowed to combine uncrossable marsh screen (309) with white forest (405) because white forest (405) isn't a screen. (In the same way as you are allowed to combine the undergrowth screens (407 and 409) with white forest (405)).

Graham

[Scott]

Ach, I should have spotted that 405 was missing from that table - my mistake. Thought it seemed a bit weird

[geomorph]

310 (crossable marsh) "should be combined with vegetation symbols to show runnability and openness...".

Do you need to show runnablility in an uncrossable terrain eg 309? No. All you need is an openness factor, as an aid to navigation.

ISOM 2000 allows 309 terrain to be seen as forested, scattered trees or open, and correctly simplifies the range of symbols allowed to be combined.

When used with 309: white 405 stands for forested; 404 for scattered trees and 403 for open, untreed. None indicate runnability - 309 does that itself.

It is interesting that ISOM2000 allows the mapper to use 401/2 instead of 403/4 for legibility reasons when in combination with 310. Wonder why they did not use 401/2 then in combination with 309?

The flooding extent periodicity that Greywolf's excellent draft points out shows why using the marsh symbols are appropriate rather than treating your lake extension as lake. Such frequencies are found in many freshwater marshes/lake margins too.

[Red Adder]

Whilst its definitely not marsh (not visible tufts of vegetation - just large oaks) changing the lake extension in to a permie marshlike symbol but using the same blue as the lake does seem to work. An explanation will appear in the key and final details. What do you all think ?

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[Becks]

I think that makes perfect sense.

[andypat]

Apparently oak trees thrive in that sort of situation!

http://www.petermoulder.co.uk/theenglishoak.html


I think its a good idea to give out some further information in the key, particulrly if the courses skirt the area as I guess around the edges it may not be as obvious? Also bearing in mind the differences between this symbol in ISOM (uncrosable) and ISSOM (forbidden to cross) - I assume this is an ISOM map?