Occassional thoughts about orienteering
Sunday, September 02, 2012
My current "rule of thumb" for MTB O trail mapping
I spent some more time working on an MTB orienteering map. The map clip shows some of the trail network.
I've been struggling a bit with the mapping. It is tempting to draw lots of variations in the rideability of the trails. As a trail alternates between faster and slower (usually due to rocks on the trail), it would be easy to over map the changes.
For my current project, I'm mapping trails in three categories. The clip above shows all three. The dominant category is the fastest riding and is shown with the longest dashes. Slower riding is show with shorter dashes (see the area labelled "B") and the slowest riding is show with very short dashes (see the area labelled "A").
To try to avoid over mapping the differences I'm following a "rule of thumb." Specifically, I don't draw a change in unless it covers an area at least as wide as my thumb (on the 1:5,000 map I was using to fieldcheck this represents about 120 meters on the ground).
I make an exception for the areas that are extremely slow. The area labelled "A" above is short, maybe 50-60 meters, but is quite rough. If I were biking it, I'd have to get off and push the bike. I suspect a better rider would be able to ride some of the areas I've mapped as extremely slow.
Back to okansas.blogspot.com. posted by Michael | 2:01 PM
I think it's important not to change the ridability too often. The rider wants to know how fast he can go from one trail crossing to the other and doesn't use this information to navigate.
Sometimes it might be useful to use the pink "bar" symbol too. This indicates when you have to get off the bike, usually to cross a lying tree or pass a barrier. But this weekend we also had it when we had to cross a stream (see here north of #2 or in the circle of #19). I had to get off the bike, while some riders might be able to bike it. I still found it a good way to show a technically difficult passage.
What I find difficult in the example you show is how to prevent people from cheating (thus going off trail and cutting the switchbacks). This will require very careful course planning.
I'm trying to avoid changing the rideability often, but I'm not sure I've figured it out yet.
I noticed a few places where a purple bar would have been good when I was out yesterday. All but one of those was a fallen tree (from Hurricane Issac which came through Kansas last week). I can imagine checking for fallen trees a day or two before an event would be a good idea.
I don't think cheating will be a big problem as long as I make the rules clear in advance. I'd thought I might make a few areas where cheating would be allowed - perhaps mark some places where it would be allowed to go off trail to connect to another trail. I would then mark them on the map and streamer them in the terrain.
I haven't competed in a MTB O' event. It looks like fun, but we don't have any of that going on around here (and very little in the US as a whole). I figure the first step is create some maps and do some training sessions. I've been thinking that a summer MTB O' series around here might work.
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Purple bar - I was looking at a local map with the possibility of mapping it. To do so, I reviewed the isom specs for MBO which includes no reference to a purple bar. Can you provide anything substantiating this symbol. I agree it would provide useful input for the rider, but where did it come from?
GeorgePost a Comment
It is symbol 843 Dangerous object across tracks or paths, stairs. It is in the 2010 MTB O standards.