The Beginners Guide to Navigation
Most rallies these days are planned on the 1:50000 metric Ordnance
Survey maps. The scale of these is approximately 1.25" to 1 mile. The
basic reference for any point on a map is a six figure reference, eg 744591.
The way to remember which grid reference to read first is 'crawl before
you walk', i.e. the first three reference figures should be read from grid
markings along the bottom of the map and the last three from markings up the
side. The six figure reference gives an accuracy of position within 100 metres.
Occasionally a reference will be given with eight figures, or else a half
will be used - this is to accuratetly define a junction say, where confusion may
exist with only six figures given. An example can be seen on map 172 Bristol and
Bath (version A3). Map Ref. 707563 1/2 - the T junction of the two yellow roads
near Shoscombe. Map ref. 707563 would be the junction of the white and the
The next type of instruction gives directions associated with a reference,
e.g. WSW734589NW. This shows you approaching the crossroads from West of
South West (Upper Hayes) and departing to the North West (down the yellow
towards Combe Hay). A series of references can be given, out of order, in the
following manner: From control 734589NW pass through the following references,
which are not in order, using coloured and white roads, and not going back on
your route: 721 1/2 603 : N730604 : E715617 and finish at control N716595. Your
route should up the yellow, into Combe Hay village, left up the white, left
down the white past Week Farm, right up the yellow to the school, through
Middle Wood, right up the white, down to reference 721 1/2 603 and down the
white to join the A367 lOOm North of the control point. It may be possible to do
it a different way, but the way shown is the shortest.
Places may be specified as being a distance from a map reference such as:- go to
crossroads 6Km from 681630 1/2 and 2Km from 735594 1/2. You should be at map ref
718583, the entrance to the white at White Ox Mead. Although two positions are
possible from these instructions, if you plot the other intersection of the
two distances you will end up near Sulis Manor and not at a crossroads. Of
course you will need a pair of compasses to plot these references but the scale
is easily taken off the grid lines which are 1Km apart.
Pictorial route directions may also be used, the best known method probably
being the "Tulip" diagram. This first appeared on the Dutch Tulip Rally many
years ago. The principle of this method is to show a diagram of all road
junctions on the route. The diagrams show the junction as it is displayed on the
map, rather than how the driver sees it. The dot shows the direction you arrive
from and the arrow the direction to go. Route instructions would be shown :-
Start on A road at 710582 1/2 NNE and follow route shown using only coloured
roads (no whites) and finish at next junction after the last instruction.
Your finishing point should be 715589, which is the first junction shown on the
Another method of pictorial representation is the "Herringbone" or "Straight
Leg". The principle is quite easy, you drive along the centre line of the
diagram, and the branches off each side are junctions you pass on the way.
Convention demands that coloured roads are shown as solid lines and whites are
shown dotted. As with tulips you start from the spot.
An instruction shown :-
could mean pass a road on your left, or it could also mean right at T junction,
turn right off road on which you are proceeding, fork right, or even hairpin
right. Whichever it is all you have to remember is - stay right and leave a
road on the left - they all mean the same on a herringbone.
An instruction shown :-
can mean pass two roads on your left, but it is more likely to mean turn right
at crossroads. The following example should make everythimg clear: Start 705 1/2
600NW and finish at crossroads following last instruction, using all classes of
Your route should take you through Nailwell and into Inglesbatch, where you go
around the small 'white' triangle. It then goes across the A367 past the PH and
then turns right down the white - note the small white near the junction with
the A367. You should then have turned left down the A367, gone straight on past
the staggered junction, past the two whites on your left - which was the very
small loop at 716592. That small loop is probably a lay-by created when the bend
in the the road was straightened, but it is the type of white an organiser will
put into a herringbone to confuse you, so read your map very carefully. The
route then finishes at the next cross roads, ref. 714 1/2 589. The two figures,
126 and 55, are spot heights which are passed along the route and serve as
checks to confirm your map reading.
Necessary equipment and more complex navigation
When taking part in an event you will need to equip yourself with the following
Mathematical forms of route description:
- FALSE ORIGIN GRID REFERENCES
You will be given a point which becomes the
origin of an imaginary grid, i.e. its reference is assumed to be 000000 - Grid
references will then be quoted relative to that false origin. You have to locate
the origin on the map and determine its TRUE map reference (if you are lucky
you may be given the map reference). To the true reference of the origin you
then have to add the false grid references of the individual points you have to
determine (remember the two co-ordinates of the reference and add them
separately). You then have the true reference of the points.
Example: Starting from 789 1/2 860NW and using the most westerly airshaft of
Sodbury railway tunnel as the origin of a false grid, visit the following passage controls (PC)
PC1 038 063 1/2
PC2 010 1/2 082 1/2
PC3 993 095
PC4 007 1/2 101 1/2
The true map reference of the false origin is 758 l/2 814 1/2.
The true reference of PC1 becomes:
PC1 is therefore at 796 l/2 878
If you work out the remainder yourself on OS Sheet 172 you will find the route
takes you from Dunkirk, through Hawkesbury Upton back to the A46 and to
Hillesley, Little Tor Hill and Wortley.
- MID-POINT OF TWO GRID REFERENCES
Example: Starting from 657863NE visit controls
at the mid-points of lines joining the following pairs of grid references.
PC15 769903 & 569863 Depart ESE
PC16 706867 l/2 & 640919 1/2
TC17 666899 & 720914
Obviously you can plot the pairs of points, join them up and bisect the line.
All very tedious and your map ends up looking like a spiders web. Think a little
longer - there' s nothing to stop a nasty organiser giving one or more points
off the edge of the map you are actually using. Calculate the mid-points by
adding the two references and dividing by two ( remember to keep
the two co-ordinates separate ). thus:-
Divide by two gives 669883 which is PC15.
The route takes you through Itchington to Tytherington (note direction of
departure) then to Baden Hill, Priest Wood and Cromhall.
- CROSS COUNTRY POINTS
Example: From Time Control 17 (see previous examples) proceed as follows:
1.35 Km N and 0.55 Km E (PC18)
O.7 Km N and 0.45 Km E (PC19) approach NW
1.75 Km S and 1.6 Km E (TC20)
Obviously you can follow this quite simply with a scale, though that way the
errors creep in in the second decimal place, and they are cumulative. It is more
accurate to remember that the grid squares are 1Km square. Thus the second and
fifth figures of a reference represent kilometres of 'easting' and 'northing'
respectively. You can therefore add or subtract distances on a map reference.
TC 17 is at 693906 1/2, therefore PC18 is at easting 693 + 0.55 Km = 693 + 005
1/2 = 698 1/2, and at northing 906 1/2 + 1.35 Km = 906 1/2 + 013 1/2 = 920. The
reference of PCl8 is therefore 698 1/2 920. Remember when going South or West
you have to subtract.
The route takes you North from Cromhall, past Leyhill to the B4509. (Note
direction of approach - you do two sides of the triangle). Then South East
through Tafarn-bach to Churchend.
- GRID SQUARE TRACES
A variation of the 'tulip' idea, but this
shows you all the roads in a full grid square. Like tulips they
can be either in-order or out-of-order. They may or may not show
all the squares you have to travel through. Example: From TC 20
proceed to the controls shown in the grid square traces shown, in
the order given.
Grid squares shown are 7290, 7293, 7493, 7392. Look carefully at
the location of PC 22.
- GRID LINES
These can be used as a means of defining your route,
and in such cases you cross each grid line once each time it is
listed (and no others), and in the order given unless otherwise
stated. Example: From TC 30 at 419911WNW proceed, using coloured
roads only, to TC 31 crossing only the following grid lines
92 42 92 92 93 43 93 44 92 91 45 91 - TC 31 is at the next
From TC 30 you should turn right off the A48, pass through
Whitebrook and Talgarth, then turn left at T. Here yau have a
choice of three roads on which to cross grid line 93 - a look
ahead to the next line to cross, 43, will help decide. Take the
road along the west edge of Wentwood Reservoir and you can then
cross grid line 43 by the PC, on either of the other roads you
will encounter line 42 or 94 first. The route continues to
Llanvair Discoed, turns south, then left at T to TC 31 at 455914.
- SPOT HEIGHTS
These are dots on the map with figures beside them
showing the height above sea level in metres. In general you
should pass the spot heights listed in the order given, and no
others. Example: Depart N from TC31 and proceed to TC32 at 477904
passing only through the following spot heights:
To avoid any route crossing SH 27 should he approached from, the
North, so turn left at the first junction, right on the edge of
Llanvair Discoed, and right again through Great Llanmellin,
safely bypassing SH 37 which if you look closeiy is a little way
up the yellow on your left. Then left down to the A48, west
through Five Lanes, via Carrow Hill and down to Magor. Proceed
east along the B4245, using the white to avoid SH 11, then left
at the outskirts-of Caldicot and via Brockwells and Caerwent to
- MAP TRACES
You will be given tracings of just the roads to be
followed, split into sections, which need to be fitted to the
pattern of roads on the map. The tracings need not be presented
at the correct orientation. Example: Depart ESE from TC 32 and
proceed to the controls shown on the following map traces.
Your route goes through Crick, Coalpits, Shirenewton, Mounton,
down the white by New Hall, to Hayes Gate. Note carefully the
locations of PC 33 and 34.
The methods described above cover the basics. Devious organisers
frequently set out to complicate things, for example leaving dots
and arrows off 'tulips', showing whites as solid lines on
'herringbones' or drawing them as a mirror image so that right
becomes left and vice versa, or stringing together a list of grid
lines mixed with spot heights and even contour heights which can
be extremely difficult to trace. Other methods of route
description specifying only directions of approach to or
departure from junctions, in more obscure cases by using the
hands of a clock face, etc., can be used. To make life more
difficult organisers may also disguise the basic route
definitions described above, by using rivers, boundaries, railway
lines, footpaths, etc , as the basis of map traces or
herringbones. In fact, anything that appears on the map can
potentially be used as a basis of a route definition, so it's a
good idea to study the map and legend thoroughly to become
familiar with all the features and symbols.
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