Discussion: tell me about mapping

If anyone here is involved in preparing orienteering maps could you describe what the field work is like? What processes and equipment do you use to collect data? How long does it take? How many people are usually involved?

One person starts with the best basemap available, and walks around the area looking at every little thing and deciding whether it belongs on the map and if so, how it should be depicted. If the basemap is excellent, then very few changes need to be made. If the basemap is lacking, or if the terrain is complex, then there's more work to do, which could involve a bunch of compass sightings and pace counting to put objects in the right places, or with more modern equipment, there could be assistance from GPS. But in any case, everything on the map has to pass through the filter of human judgment, including the shapes of contours. Traditionally the mapper basically drew the entire map with colored pencils (at an enlarged scale), although increasingly mappers bring some sort of tablet computer into the field and do the CAD work directly, rather than indoors after they get home. This saves duplicating effort, although there is the risk of falling to the temptation of just leaving the basemap unaltered.

A mapping project can be split up between multiple mappers provided they are in agreement about the mapping standards to be used (how big a boulder needs to be to appear on the map, how thick vegetation needs to be to be a certain shade of green, etc.). And sometimes mappers split up a project without being in agreement, which can result in a somewhat odd and inconsistent map.

In this modern age, all orienteering maps are drafted using a CAD system. 0CAD is by far the most common choice, although not the only one.

The science of getting mapped objects in the right places is not that hard, but the art of knowing what to map and how to represent it is the more challenging part. It requires the eye of someone who has some experience with orienteering maps, who knows what a map should look like, and who has some inherent talent for this. Some novice orienteeers are surprisingly good mappers, and a few excellent competitors never really get it.

Lots of time and patience, and sometimes a thick hide.

Years ago, I seem to remember the time in the field for an experienced mapper to field check an area as 40 hours per square kilometer. That may be wrong and I'm sure it depends greatly on the terrain and the quality of the basemap.

From a novice mapper who did his first attempt at mapping a local city park: walked the park during winter months when there is no foliage, with a clipboard and enlarged color copies of sections of the map. Looked for and mapped rock formations, boulders, cliffs. Also included some man-made features such as fences, posts, ruins, stone walls, pits, depressions, springs, obvious clearings, power lines and poles. On a second pass, and this part was the hardest, judged what should be in terms of vegetation (aka runnability) and made an decision on what earned a patch of terrain to get one of the three levels of green, and marked it on the paper copy on the clipboard. While all was pretty fresh in memory, tried to edit the OCAD file as soon as possible, possibly the same day. JJ is right when he mentions "art": sometimes I found a nice stone wall right next to the trail edge, but including it on the map blurred the area with a thick black line that ended up smudging other features, and besides, it was basically part of the trail.

In addition to the base map & compass, I also use a laser range finder. It saves me a lot of time from having to measure distance and is very handy in areas where it is difficult to walk straight like steep hillsides or thicker vegetation. I have also increasingly been using a GPS but you have to be very careful as the GPS isn't always accurate enough, at least in the parks I have been mapping.

You do have to be wary of those rangefinders on those steep hillsides. The rangefinder will give you the actual distance between where you are and the point you are plotting. The map will want to show you the relative distance as if every point on the map were on the same plane of elevation.
For instance when two golfers at our club, one with a rangefinder and one with a GPS unit measure the distance to the centre of the green on any hole there are significant differences in the two measures when there is a change in elevation involved . As the slopes get greater so does the differences in distances measured.

What kind of differences are you seeing? Can you give a typical example? Off the top of my head, it seems like it would take a pretty serious change in elevation for that to be an issue. Percent elevation changes tend to be less than people expect.

if you are going to use a rangefinder you need one that can calculate horizontal distance - they cost a bit more I think

I don't use rangefinder, but I suspect these slope-error concerns are a bit overblown for the beginning mapper. (In fact, I'd wager that the GPS rangefinder has more trouble with steep grades than the laser rangefinder). Even on a really steep slope (say 25 degrees), the laser rangefinder should only by off by about 10%.

If the aerial photography is not orthorectified really well, it's easy to get 10% distortions on your basemap. If your basemap is distorted, you're pretty much stuck with it. Good luck correcting that kind of distortion from the field.

The key to a good orienteering map is relative accuracy though. Competitors won't care about a few meters of error in the absolute position of an object, so long as it is placed correctly relative to all the other nearby objects. Hopefully, you'll always have a few solid reference points on your basemap that are less than 50 m away. Use the rangefinder to check location relative to those, and if you're within 10% error, you should be golden.

The one thing you have to be on the lookout for is closure and consistency. You might determine the location of a feature relative to two or three different reference points, but these measurements might not agree perfectly. (Maybe due to measurement error, maybe due to distortion of the basemap). Then you have to do a little triangulation, and find the best compromise position to place that feature.

One of the skills you build as a mapper, is figuring out which relationships are most important and reliable when you make those compromises. Absolute position is important (especially for making maps that can be easily revised later). But you should also think about how a navigator sees the terrain. Think about how a competitor might use height on the slope, angle from the trail junction, or distance from the vegetation boundary to attack that feature.

I used a range finder a lot. Mine has a bubble level, so measuring level was no problem. There were places in Taiwan where there was no way of walking, thus pacing straight to a boulder, etc. due to a myriad of vines on the ground, clusters of bamboo, etc. Red laser view-enhancing glasses were definitely a plus on bright, sunny days. These measurements were definitely way more reliable than the GPS when in the forest, as the vines foliage on top of the tree canopy was often way to thick.

You can deal with the problem using range finder on the steep hill sides.
Take your measurements from top down. Measure it to a tree at your eye level.

Thanks everyone for replying. Mapping sounds like something I'd really like to do but I'm still a beginner at orienteering - do you think this would be a problem? I'm not sure whether it would be cheeky to ask to get involved at this stage...

Also, is OCAD like AutoCAD at all?

Start with a Metro map where 90% of the map is olive green.

You may find that OCAD is different from other CAD and drawing programs. But it is free to try and you'll get lots of advice on the web.
https://sites.google.com/site/juniormappersguide/

You can also join the "O-map" Yahoo group:
http://groups.yahoo.com/group/O-Map/

With the risk of repeating what has already been said, my advice about mapping: Try to find the best basic documents:
1: Ortho photo lidar, or if what you find is welcome.
It's best to contact a profesionst to help you for choosing documents and their corroboration.
2: If you want to then doing other maps, are keen to avoid gadgets. Compass and your steps are sufficient for the first stage. Then, you can complicate your life as much as possible with all existing gageturile
3.Nu is a problem if you have no experience in maps, or you're the best orientarist: I know the only difference between a good or bad cartographer, time spent on the ground.
so if you have time and your determination is great, it will be ok.
4. no number limit for mappers. If you have the chance to have someone with some experience around you is perfect, if not at least try to have a distinct limit f great among you: (road, river, cultivated land, etc.).
5. by far the best program for drawing, it OCAD.
But cost. Unless you want to pay, there are alternatives:

http://dl.dropbox.com/u/2113380/OO%20Mapper%20pres...

If you have not yet drawn with OCAD, why not try with it?
Good luck!