Using lines of position to fix your location on a map

[Jeff McWilliams]

Ray J – one more:  attack point

I’m going to follow this trail until it crosses the next stream.  The place where the trail crosses the stream is my attack point, where I will then follow an azimuth (or bearing if you prefer) of 35 degrees for approximately 500 feet until I reach my hunting blind.  If I start dropping into a steep ravine (catching feature), I know I’ve gone too far.

 

[Jeff McWilliams]

one last comment.
If you’ve never heard of it, go search “Route to Christmas” or visit the 2020 collection at http://news.worldofo.com/rtc/?year=2020

These are case-studies in pro-level orienteering competitions, where picking a route that shaves a minute or two off of your travel time can make the difference between winning and losing.  It can be pretty mind blowing to understand all the factors that go into a good route choice vs a great route choice.

Is it off-topic for backpackers?  Not necessarily, especially for those who are aiming to do a “high route” or similar off-trail travel.

[Roger Caffin]

Hi Jeff

But have you tried one of them?
I do not need a declination adjustment: I simply correct the bearing in my head.

Actually, both of those compasses I mentioned do have a very simple declination adjustment on them: a rotating ring and grid. I line up the compass arrow with the rotated grid and it is all done. I don’t need anything more than that.

I would never walk a mile without looking at the surrounds anyhow. I use the topology as much as the bearing for navigation. Did that once in a serious snow storm over many km and came out spot on the bridge we had to find. YMMV.

Cheers

[Ray J]

Jeff M,   Great point.  There’s even an Orienteering Forum called “Attack Point”.

Roger C.  Yes the surroundings and the terrain are incredibly important.  Our Orienteering classes even point out that the MAP and understanding how it relates to the terrain is more important.  “Thumbing” the map in Orienteering speak.  So your thumb (or the pointer on the compass) is at the last land feature/map point where you knew where you were.  I do advanced, but short orienteering courses about 15 times a year.  Plus I do course setting work for our club.  About half my “legs” are done with only a rough compass bearing, because I’m focused on the terrain as I pass it.

Route choice is also very important.  And knowing what you do best!  I will often look for the easier way around something, even out of the way, instead of trying to go thru tough terrain or needing a compass bearing.  “OK…I can try a fine compass over this terrain with no handrail and not much to note, OR I can go around a bit, hit the stream, follow the stream to that big bend which the map shows is a earth or rock face then, I’m 80 percent of the way on my travel”.

[Roger Caffin]

I will often look for the easier way around something, even out of the way,
Chuckle.
I remember one ’24 hr walk’ (a race, point to point, collect tags at the points) where the ‘obvious’ route was across two gullies, and the ‘long slow’ route was a big loop around on a road. Hehehe: the gullies were really chock-full of blackberries!

Cheers

[Jeff McWilliams]

Roger – I’ve been in one of those races!  It was a 6 or 8 hour race down in southern Ohio and oh boy, the briar patches down there were brutal!

Simple compasses and declination:  so I lead a map & compass workshop through our local outdoors club every year, with 8-16 participants each session.  We have a bunch of the cheaper compasses, though I’m not sure exactly which brand they are.  We teach the mnemonic for doing the declination adjustment mathematically:  “map to compass, map to compass, map to compass, east is least & west is best”.

We also demonstrate how to draw new north-south lines on the map that are aligned to magnetic north, so that rather than adjusting the azimuth on the compass, the declination adjustment is already built into bearings measured on the map instead.  (We do this on A4 1:24K maps that we print up for the workshop, not big 7.5 minute quadrangle maps or commercial maps.)

Given all these techniques, I much prefer setting the declination on my Suunto and forgetting about it.  That’s even more true when doing 6-8 hour adventure/orienteering races where I may be transferring azimuths from the map 20-50 times in a single race.  When I’m tired, I just don’t want to have to deal with the extra mental load of adjusting for declination manually.  I prefer to let the compass do that part for me.

Also, do those cheap compasses have a global needle?  I’m not sure they do.

 

Ray – Attack Point is awesome.  SMOC (Southern Michigan Orienteering Club) is on there.

[Roger Caffin]

We also demonstrate how to draw new north-south lines on the map that are aligned to magnetic north,
Ah, OK. All our topo maps have a little compass rose on them indicating Magnetic North, Grid North and True North. We get used to allowing for the magnetic declination automatically. I do photocopy the topo maps for field use, but we don’t need the reminder any more.

do those cheap compasses have a global needle
They probably do, since they are selling the same ones around the world.
I know that the compass mfrs used to weight the needle slightly to make Southern Hemisphere and Northern H versions, but that is really not necessary if you slightly redesign the pivot. All you have to do is to lower the centre of gravity of the needle a few mm below the actual pivot point. Gravity does the rest.

Cheers

[Ray J]

Chuckle…  Roger C.

At one of my favorite venue’s, Tyler State Park, Texas, this last spring, I was moving and thought I could cut a switchback off a trail.  At my map scale of 1:10,000, I didn’t “See” enough of the detail and had not been in that area in a number of years.  The switchback went around not one, but TWO almost vertical cliffs down to a minor stream.  I got down and up the first area, but the far side was full of Texas Briar’s (hard to describe, bring bandages).  I looked down the next and GULP.  I started tracking South to hit back to the switchback.  If I’d stayed on the trail and done the switchback it would have been some minutes faster even going out of the way.

The Pre-Covid event at the same park, I was in a different area and looking at a 10 meter area of dark green.  Dark green on our Texas maps is “Do you really think you can get thru this?”.  But hey, 10 meters! And I’d hit a paved park road.  Save about 50 meters of climb out of the gully system.  Well, that 10 meters was actually a marsh and the dark green was about 6 inches of vines on top of the marsh and 14 feet tall bamboo and marsh grasses.  Funny thing, I was about at a dead stop trying to push thru it and heard someone off to my side.  I felt better as I wasn’t the only one trying it.  The course setter (A friend) had a good laugh when I told him what I’d tried.

[AK Granola]

Our topo maps are so old that the printed declination is incredibly off, can’t remember just how much. Plenty far enough to get you lost if you relied on it. But I’ve gotten lazy anyway because the map alone is usually sufficient.

[Roger Caffin]

Hi Ray

Yeah, we know the feeling. Some of our 1:25k topo maps were done during the war, in a hurry and from limited aerial photos, and they have not been updated. They tend to miss a few ‘features’.

We had been trying to follow a fire trail or 4WD track shown on the topo along a very remote ridge. Well, we could see where it used to be: a slight dozer blade scrape on one side, and a solid wall of young scrub in front. This was NOT going to work. (Turns out it was dozer line put in during a fire long ago, and never maintained.) My Ranger friend knew about it, but had never expected anyone to try to follow it!

We were up on the sandstone plateau, where there is no water period, so we thought we would go off the side down what looked like a decent side spur to the creek below. The topo map suggested it was a very gentle even slope all the way.

We found the spur off the ridge all right (in the dense scrub) and started to follow it towards the creek below. The spur was actually fairly easynce we were on it, being mostly flat and with little soil for scrub. No problem! Ahhh – maybe TOO flat?

Then we got to the end of the spur – the end on the ground, not on the topo. Ah yes, well, maybe not so good. About 30 m of vertical sandstone cliff all around. Oh dear, but not really unexpected in this country. There are cliffs everywhere, but none on the map.

We had some water, so we camped. Excellent views, mind you: the top was quite flat and open. Soft flat site too.

Next morning we back-tracked a bit to where I had seen a wombat poo the night before. What is so special about that? Well, wombats need access to water (like humans), so I knew there had to be a way down to some water not far away. We carefully followed that wombat track through the scrub and cliffs to the crest of the ‘gentle spur’ below, and had morning tea on the very pleasant creek at the bottom. The cliffs looked just as bad from below.

Cheers

[Author]

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