Discussion: Mapping compass tips?

Anyone have any tips for a mapping compass? I've had a few of the Silva/Brunton 54LU, but they keep failing (needle bearing falls apart) and aren't cheap! I love the sighting system though. Can't really imagine mapping any other way.

Using a sighting compass is slow as. I use an invention by John Bowler who used to make maps for OAWA. It's basically a protractor mapping board. I'd attach a picture but as far as I can see you can only insert url's to posts in AP.*

I'll email you the photo instead.

*Maybe someone can tell me how to attach a file, such as a photo.

To insert an image, you can try:
<img src="url to your image" />

works on my log

You just need to have the image on a web page somewhere (photo pages like photobucket, flickr, etc... work), then use the coding that simon posted. Try to make sure the image size is only about 400-500 pixels wide (~4").

I'd like to see that photo too.

Thanks for the photo, simmo. I'd post it if I had some web space!

I use a thumb compass with a rotating housing. Rarely take sighting bearings unless white paper mapping.

I don't map enough to call myself a mapper, but I do have the compass you have, a Silva/Brunton 54LU.

I found a Suunto KB-14 on ebay for about half of retail price. There is also a Suunto KB-20 which is cheaper, but plastic. If you like sighting, I doubt it makes a difference.

I'm aware of three methods to transfer angles to the map:

1. A board with north lines and a compass.
2. A sighting compass.
3. A long baseplate.

With 1, you line up the compass to the north lines and draw the line by eye.

With 2, you read the angle, and then use another tool to transfer that angle to the mylar. (With the Silva/Brunton 54LU, you can use the capsule to transfer the angle.)

With 3, you aim the baseplate at an object, turn the capsule to north, and then use the compass itself to draw the line on the mylar. Moscow Compass makes a long mapping baseplate, but I can't find an image of it.

I have used all three, but I'm not even close to being an authority. I like 1 for adding details in a small area. I like 3 for the additional reassurance of getting farther objects a little more accurately. I tend to use 2 for when I want the best accuracy for stuff that's really far away. The additional step of transferring the angle to another tool adds time and the possibility for error.

I know people who swear by 1 and think the other ways are a waste of time. I also know people who do 3 all the time and think 1 is too inaccurate. For me the biggest issue is the quality of the basemap. If it's good, you don't have issues with long-distance alignment. But if your basemap is bad, you need to be careful lining up distant features.

(If you send me the photo, I can host it and provide a link to it.)

Andy,
The website that cedarcreek pointed out has a lot of sighting compasses. There is one that is similar to the yours, but it costs the same amount. Maybe you should try a mirrored compass, then you would have the angle set when you do the aiming. However, the needles on these compasses are probably not so good. If you could stick a mirror on a jet, then you would have an ideal combination.

http://www.thecompassstore.com/sighting-compasses....

For you others, if you ever get a chance to run on one of Andy's maps, you should do so. He is an excellent mapper.

I would stick to the sighting compass. I use the Silva Sighting Compass Model 54 and I am satisfied. With this compass you get accuracy +- 0,5 degree. With normal compass maximum +- 1 degree.

You don't need that level of accuracy for an orienteering map.

Let's imagine a feature 100m away at 90 degrees. If the true bearing was 89.5 degrees, the feature would only be .87m away from where you thought it was (100x2xPi/720). To draw the new position on a 1:15000 map, you would have to move the feature by less than 6/100 of a millimetre, and it wouldn't really matter.

In a complex area it's more important to get the key features looking correct in relation each other, than have a very strict (less than 1 degree) level of accuracy.

Running orienteers cannot consistently use the compass with much more than 95% accuracy, so +- 1 degree by the mapper is more than adequate.

olles and andyd---How do you use the sighting compass? Do you use the 54 to draw the line on the mylar, or do you use it only for sighting and use something else to draw the line?

When I've tried to use the 54 sighting compass (there are non-sighting 54s, too), I tend to keep the capsule set to N and then sight through the mirror East-to-West. Then I set that number into another compass to draw it. It just seems clumsy to use just the 54---it's like I'm always turning the capsule, then turning it back to sight again.

When I first started mapping (1980) I used a 54, and I had exactly that problem. I soon realised that I could map most features better by fixing a compass to my map board, and then I only used the 54 when features were further apart (60m+). Occasionally, I would take a back sight just to confirm the accuracy of a key feature. When I got my mapping machine (see post 2) I didn't need to use the 54 any more.

With sighting compass you read the angle, and then use the same compass to transfer that angle to the mylar.

Thanks for the thoughts everyone. I've always used the 54 by sighting the bearing then dialing it up and plotting it with the same compass. Two compasses sounds more awkward than turning the housing on the one back and forth. My first attempts at mapping were with an ordinary baseplate and a poor basemap, so errors would compound themselves as the map grew. I found I'd map myself into a corner where nothing fitted. Then I realised that my bearings were often 5 degrees or so off. The 54 was a revelation! I would like to try what simmo describes, though.

If you do use the 54 for sighting and also wear glasses with steel in the rims, be careful to hold it away from your face when sighting or the bearing will be affected.

Here is the protractor mapping board simmo mentioned:


(click for larger image)

simmo wrote:

"The white disc (the drawing board - plastic with a white backing) is attached so that it moves through 360 degrees - you turn it using a knob on the underside. A piece of base map 500mx500m (at 1:7500) is taped to it, with a piece of clear film to draw on taped over that. It does have North marked, and North lines, but they're pretty faded (the board was made in 1986) The base map is taped so that it is aligned to magnetic North, and the North lines should also be drawn on the clear film so that you can match the pieces up. 500m x 500m (1/4 of a sqkm) at a time sounds very small, but in an area of very complex terrain it's the best way to work.

"The compass is any old basic Silva that still works. It is glued on to a clear plastic base that serves as a protractor, as a sighting extension and as a ruler for drawing (eg faint lines that can then be paced off - see below). NB I am left-handed - if you are right-handed the compass base would be the other way round!

"The compass base is attached to the small piece of wood, set in a groove between two raised bevels. The top bevel is 'floating', so that an elastic band at each end holds the compass base firm, but not too firm, and it slides easily across the board.

"Underneath is a handle (comfortably fits my right hand!), and the knob for turning the disc, which can be done by two fingers of my right hand.

"To map, you first identify and draw features from the base map. To map features not on the base map, simply point the board towards them while standing at a known feature, orient the board to North and draw the feature in - or if it is more than say 30m away, draw a faint line to it, then pace the distance off, then draw the feature in. Linear features can also be drawn in this way. As you put more features in, triangulation serves as a double check.

"I am trying to contact the inventor, John Bowler, to see if he has any detailed construction plans."