YOUR MAPS – Whence Commeth They
When we talk about mapping I think we ought to break it down to separate operations. There is the Surveying part and the Cartography part. I won’t say too much about the cartography part as the usage of the well known OCAD system of computerized map production is a skill well beyond me and the execution of it limited to a few really qualified computer experts. We are lucky enough to have one such in our club and he, Bill Brown, also takes part in the surveying process.
We may start from a base of
a. An old orienteering map.
b. An Ordnance Survey map.
c. A photogrametric plot.
This last we have not yet done but in very contoured country it would be a lovely option to be able to use this pre-contoured base.
The base map is scanned into the computer and nice A4 sheets of the area are printed out in ‘shadow’ form to use when actually conducting the survey. Care is taken at this point to ensure that the 100m grid superimposed on the output sheets is corrected to magnetic North. Remember magnetic North is a steadily moving position so this correction is really necessary. We generally use a scale double that of the printed map, eg, 1:7500 if the map is to be 1:15000.
Be prepared to go out in the field in all weather conditions except continuous rain with sensible clothing and a compass, and pencil and rubber. As you are likely to be on your feet for anything up to six hours be comfortable and in our case in this part of the world it seems to mean waterproofs all over, plus bogtrotters. As you are going to need a break take a pack lunch to eat in the car at that time.
The Survey System.
Armed with a sheet of the area in shadow format and with its 100m grid start by addressing one section of the map, for instance a part bordered by good line features like large tracks.
Now the interesting, tedious, tiring, satisfying, decision making time commences. Basically it is a question of covering the area, adding to and altering the base sheet as you pace count always on a compass bearing to pick up every feature to be marked. It is not easy to describe as every situation is different. Perhaps a snapshot of a contrived example could help. So, PC =pace count and C=on a compass bearing.
Thus a. C,PC down major track -find distinct vegetation boundary joining track.
b. C,PC along boundary to see a depression off to one side.
c. C,PC off boundary to depression. Return to boundary where you left it.
d. C,PC along boundary to find a track.
e. C,PC go along track to find a track junction.
f. C,PC from junction back to that depression, thus double checking its position.
And so on, seemingly endlessly !
Whilst doing this you make decisions as you go and mark them on your map. In the above example you would in passing need to:-
- Decide on the runability of the ground beside the track, on each side of the
boundary and each side of the track.b. Decide to show the depression as a large or a small one.
c. Decide what size of tracks you will allocate.
d. Decide whether to put dots along the boundary or not.
So you can see it’s not just marking things in the right place but deciding things like runability, eg, will you make it ‘slow run’ or ‘walk’, and achieve consistency throughout the area. If two are surveying it is very difficult to get consistency of standards. The decision about what level of detail you put on the map is always a conundrum. Put in too much and it’s cluttered and unreadable, too little and it’s bare and the situation is worstened if the map is to be printed at two different scales !
The 100m grid superimposed on the map is most helpful; in fact we don’t think we could do without it. You do need to have your pacing system well sorted and the compass is generally used in the way of being a sighting compass. You can use a proper sighting compass or even an optical sighting device that reads out distances, if you can afford such a luxury.
Each of the survey sheets is scanned into the computer and superimposed on the existing map from which the survey sheets emanated. Then all the updating, alteration and modification can commence using the OCAD system.( the black art curtain descends at this point)
When this is done each survey sheet is printed out and the author of the survey sheet checks closely to see that all his squiglings have been correctly interpreted and marks up any errors.
Finally a sit down session next to the computer to actually make the noted corrections thus giving the non-cartiographical member of the team an opportunity to see the OCAD system in operation – fascinating in it’s power and complexity !
The cartographer now completes the map with all the peripheral information and pretties it up for printing.
So you can see the survey business is very much an individual affair and everyone works slightly differently. There is no wrong or right method as long as the final map is sufficiently accurate and actually looks like the area as seen by the orienteer. It is a time consuming business and there are no short cuts, particularly in areas short of features where criss-crossing or going up and down on parallel lines to discover the hidden detail is needed.
The satisfaction comes when you see the completed map in all its beauty, only to be marred by the resentment of the frustrated orienteer who has failed to find his way on the day.