Transcript Ordnance Survey - Bishop Stopford School

Map Reading &
Navigation
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Introduction
This clear and simple tool is designed to
provide you with the basic skills with
which to learn to map read.
Using a step by step process, you can
progress comfortably at your own
pace, with practical exercises and
illustrations in every section to help
you learn.
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Equipment
Equipment requirements are simple.
You will need a:
Ordnance Survey Map
Silva Compass
Sharp pencil
Plain Paper
Fine String
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Course Content
• Maps
• A brief History
• Components
–
–
–
–
–
Type/Scale
Symbols
Plotting a location
Measuring distance
Relief
• The Compass
– Components
• North
– True
– Grid
– Magnetic
• Map & compass work
Route Planning & Safety
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Definition
Map .noun. Flat
representation of
the earth or some
part of it with its
physical or political
features or of the
heavens
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History
Ever since man has been able to
write and draw there is evidence
to also show that he has recorded
routes on land and sea.
Where maps were originally shown
on clay tablets and papyrus, we
can now display them on paper and
even CD Rom!
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The Ordnance Survey Map
Ordnance Survey
maps come in a
variety of
different formats
and this guide will
show you how to
choose which one is
best suited for
your own use.
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Types of Map
The importance of choosing the right map.
Scale
1:1,000,000
Map to Ground
Activity
1cm = 10km
UK Map
1:250,000
1cm = 2,500m
Use in car, motorbike
1:100,000
1cm = 1,000m
Cycling, route planning
1:50,000
1cm = 500m
General Purpose map
1:25,000
1:15,000
1cm = 250m
1cm = 150m
Standard walking map
Orienteering
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Symbols
We interpret both man made and
natural features on the map,
through a system of symbols.
Every Ordnance Survey map has a
key showing the definition of each
symbol to help you. We will look at
a few of the more common
symbols.
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Symbol examples
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Symbol examples
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Grid lines
• Every Ordnance
Survey map is
covered in a series
of grids.
• By learning to use
these grids we are
able to locate a
particular point on
a map.
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Distance
1.5 km
1 km
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• Grid lines on all
Ordnance Survey Maps
are spaced 1km apart,
regardless of scale.
• This makes it easy to
judge the rough
distance between
points by counting
squares.
Grid Lines
52
52
63
Horizontal Lines = Northings
64
51
51
50
50
65
66
Vertical Lines = Eastings
49
62
63
64
65
66
Reading a Grid Reference
• Grid references should be read in the
following order:
– Eastings
– Northings -
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Along the Corridor
Up the Stairs
Plotting a Grid Square
52
52
63
51
64
65
66
51
Stairs
The
50
50
& Up
Along the Corridor
49
62
63
64
65
66
Plotting a Grid Square
52
52
63
51
64
65
66
65
66
51
Grid: 64 50
50
50
49
62
63
64
Accurate Plotting
• Having plotted the grid Square (1km x 1km)
you will often need to establish the
accurate location of a point or feature
within the Square.
• This is achieved by dividing the square into
a further ten Eastings (Vertical lines) &
Northings (Horizontal lines).
• These additional lines are read in exactly
the same manner as before.
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Accurate Plotting
(One Grid Square)
1 km
0
9
8
7
6
5
1 km
4
3
2
1
50
0
0
64
1
2
3
4
5
6
7
8
9
0
Plotting an accurate location
100 metre accuracy
62
63
64
65
66
52
Grid: 646 504
51
50
49
Measuring Distance
By using the scale at the bottom of
each Ordnance Survey Map you can
easily convert a measurement in
centimetres into a real distance on
the ground.
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Measuring Distance
using a Silva Compass
Nearly all compasses have a centimetre
scale which proves an effective tool
for measuring the distance between
two points.
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Measuring Distance
using a Piece of String
• Trace your route on the map with a piece
of string and mark the points at which the
route starts and finishes on the string.
• Place the string against the scale on the
map and read off the equivalent distance
on the ground.
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Measuring Distance
using a Map Measurer
• Map measurers are
purposefully designed
for measuring
distances on a map.
• Trace your route with
the small wheel at the
bottom of the
measurer and it will
automatically tell you
the distance on the
ground via a rotating
scale.
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Relief
• Relief refers to
the way in which
height is displayed
on a map.
• This is shown by a
system of lines
called ‘Contours’.
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Contour Lines
• Contour lines link
points of equal
height on the map
at ten metre
intervals.
• Contours display
how many metres
land is above sea
level.
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Definition
Compass .noun.
Instrument
showing user the
direction of north
and other points
of the ~ by means
of magnetic needle
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The Compass
There are a
variety of
different
compass styles
available to you.
We suggest that
to begin with,
you use a Silva
compass similar
to the one
pictured here.
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The Compass
• They were originally discovered by the Chinese
5000 years ago.
• They are made in a variety of forms for use on
land, above and below the sea and in the air.
• Examples of activities in which they are used are:
–
–
–
–
–
Hillwalking
Cycling
Driving
Sailing
Flying
-
Mountaineering
Surveying
Military
Scuba Diving
Orienteering
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Cardinal Points
(Compass Points)
North
0º & 360º
North West : 315º
North East : 45º
West 270º
90º
South West : 225º
East
South East : 135º
180º
South
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Bearings are taken in degreesº- The cardinal points
are divided up into 360º & measured clockwise.
North
0º & 360º
North West : 315º
North East : 45º
West 270º
90º
South West : 225º
East
South East : 135º
180º
South
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Parts of the Compass
• The compass can be
broken down into
various components.
• We will look at each
component
separately to define
its use.
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Base Plate & Compass Housing
Compass Housing
Base Plate
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• The Base Plate is the
mounting for the
housing and displays a
variety of
information eg. Scale
ruler.
• The Compass Housing
contains a magnetic
bar, called the
Needle and defines
the points of the
compass on a rotating
bezel.
The Compass Needle
Needle
• The needle is
suspended in liquid
which enables it to
move freely, always
settling with the red
end pointing North.
• Some needles are
Luminous to help
navigation in the dark.
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Direction of Travel Arrow
Direction of Travel
Arrow
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• The Direction of
Travel Arrow
indicates the
direction along which
you wish to travel or
take a bearing.
• The arrow is fixed
within the base plate.
• The sides of the base
plate run parallel to
the arrow.
The Index Line
Index Line
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• The Index Line is a
fixed line within the
Compass Housing and
is in line with the
direction of travel
arrow.
• The Index Line
marks the bearing
you set by rotating
the bezel.
Orienting Lines
• These are displayed
within the rotating
Compass Housing and
are designed to be
aligned parallel with
the Eastings on a
map.
Orienting Lines
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• The orienting lines on
some compass models
show one half of the
lines in red to depict
north.
Compass Scale
• Nearly all compasses
have a centimetre
scale along the edge of
the base plate to
enable you to measure
distances.
Compass
Scale
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• Used in conjunction
with the scale at the
bottom of the map,
the compass scale
enables you to
calculate the distance
on the ground.
Points to Note
• Stand clear of metal objects when using the
compass. They will cause the needle to deviate
and create inaccurate bearings. Objects as small
as watches can make a difference.
• Hold the compass as flat as possible to allow the
needle to move freely.
• Look after your compass - try to avoid dropping or
knocking it.
• Store away from other compasses and electrical
equipment.
• Your compass may need replacing if a large air
bubble forms in the Compass Housing.
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True / Grid / Magnetic North
• True North
poles.
and South are at the geographical
• Grid North
is the direction to which all
Ordnance Survey Maps are oriented. We take our
map bearings using Grid North.
• Magnetic North
is the direction a compass
points to and in the UK it is located approximately
5º West of Grid North.
Magnetic Variation
True North
• The difference in
degrees between
Magnetic (Mag)
North and Grid
North is referred
to as the Magnetic
Variation (usually
5º West in UK.)
Grid North
Magnetic
North
5º
Magnetic Variation
• It is important to
understand the
relationship
between Grid &
Mag north as this
will become
important when we
start to convert
bearings to and
from a map.
True North
Grid North
Magnetic
North
5º
Map & Compass Work
• Having looked separately at both the
Ordnance Survey Map & Silva Compass the
following example will demonstrate how
they are used together.
• If you are unsure about anything which has
been covered in the previous slides, look
back now before you progress to the next
section.
Map & Compass Work
• When working from the map we deal with
Grid Bearings.
• When following a compass on the ground we
work with Magnetic Bearings.
• There is a simple system which enables us
to convert Grid to Mag and Mag to Grid.
• The system refers to whether we add or
subtract the magnetic variation to convert
the bearing.
Map & Compass Work
Mag to Grid…………. GET RID
Grid to Mag………….ADD
(usually 5º West in UK)
Map to Ground
Grid to Mag………….ADD
Map to Ground
• Select a start and finish point on the map.
• Line up the edge of the compass with the
line along which you intend to travel.
• Keeping the base plate static - rotate the
compass housing until the orienting lines
are parallel with the Eastings and the red
‘N’ is pointing to North on your map.
Map to Ground
• Read the bearing shown on the housing
from the index line.
• Remember - Grid to Mag……Add.
• Add the magnetic variation shown at the
top of the map (usually 5º West in UK.)
• You now have your magnetic bearing of the
course you have chosen. The next step is
to orientate yourself.
Orientating
• Hold your compass level and steady.
• Turn your body until the red end of the
needle is in line with the Red ‘N’ on the
Housing.
• The direction of travel arrow is now
pointing along the route you chose from
the map and you are ready to travel.
Following the Compass Bearing
• Hold your compass level and steady.
• Ensure that the red end of the needle is in line
with the Red ‘N’ on the Housing every time you
refer to the compass bearing.
• Follow the direction of travel arrow. You will find
it easier to line up the direction arrow with a
physical feature on the ground (eg tree, pylon,
tower). Use this as a reference point which you
can move towards. This is easier than following
the compass every inch of the way.
Ground to Map
Mag to Grid…………. GET RID
Ground to Map
• Select the feature on the ground to which
you wish to take a bearing.
• Hold the compass steady and level.
• Point the direction of travel arrow at the
feature.
• Rotate the housing until the red end of the
needle is in line with the Red ‘N’ on the
Housing.
Ground to Map
• This is your Mag bearing which you can
either travel along or convert to a grid
bearing.
• To plot on the map you should first locate
your own position and mark it.
• Convert the Mag bearing to a Grid bearing
by Mag to Grid……Get Rid. (Usually 5º West in
UK.)
• Subtract the magnetic variation.
Ground to Map
Place the compass on the map and keeping
the bearing set on the housing, rotate the
whole compass until the orienting lines are
parallel to the Eastings on the map. The
edge of the compass should run through
your position and show the bearing on the
map.
Ground to Map
By turning your body until the red end
of the needle is in line with the Red
‘N’ on the Housing you have now
oriented yourself and the map.
Quick Orientation
You can orientate yourself and the map to the
ground at any time using this easy system:
A.
B.
C.
Lay the compass on the map.
Line the edge of the compass and the
orienting lines up with the Eastings.
Turn your body until the red end of
the needle is in line with the Red ‘N’
on the Housing.
You and your map are now facing North.
Route Planning
• It is important, where possible, to take
time in planning your route before you
start.
• This will help you to identify any problems
early and to estimate how far you intend to
travel and how long it should take.
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Route Card
• A route card is simple to produce and
makes navigation on the ground simple. A
basic format is shown here:
Date: 21/07/99
Time
Grid
0900 501 412
0925
521 412
1030
521362
1045
514358
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Bearing
90º
180º
240º
300º
Number of Persons: 2
Distance
Remarks
2km
Car Park to Bridge
5km
Bridge to hilltop
1km
Hilltop to wood
1.5km
Wood to church
Route Planning & Safety
• Make sure that your route is well within
your ability and that you are in possession
of the right equipment.
• Leave a copy of your route card with a
friend or contact in order that you can be
easily found in an emergency.
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Map Reading &
Navigation
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Ordnance Survey
Romsey Road
SOUTHAMPTON
United Kingdom, SO16 4GU
www.ordsvy.gov.uk
Produced in association with
The Expedition Company Limited
Po Box 17
Wiveliscombe
Taunton, TA4 2YL
Tel: +44 (0) 1984 624780
Fax: +44 ()) 1984 629045
email: [email protected]
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