MAP READING
NAVIGATION
Types of maps
Marginal information
Scale
Ground Shape
Calculating slope
Intervisibility
North points
Measuring distance
Map orientation
What to do when lost
Fire behaviour
Grid references
2
A map is:
• A flat representation of the earth’s surface at
a given point in time
• The reliability of a map gets less with age
• A good map will give you the information
your looking for
• Have the right map for the right application
• To preserve a map, fold it correctly
What is map reading?
•
•
•
•
•
Map reading is the skill of interpreting information on a
map so that you can develop a birds eye view’ of the
country in your mind. This picture includes:
The location of roads and tracks
The shape and slope of the land
The location and type of natural features, for example
rivers, creeks, deserts
The location and type of structures, for example bridges
and dams
The vegetation type and density
4
Navigation and map reading aids
Maps
Maps are the most important navigation aid. When they are
studied prior to undertaking cross – country travel, it enables
you to appreciate the terrain, develop a better sense of
direction, and instill a higher level of confidence, rather
blinding following a GPS.
Aerial photographs
Recent air photographs are usually more up to date than
topographical maps. They do not replace maps, but when
used in conjunction with other navigational aids, can provide
an excellent source of information. Aerial photography
interpretation is a specialised skill, and requires extensive
training to achieve a high level of expertise.
5
Types of maps
- Topographical maps
–
–
–
–
–
–
–
–
–
• 1:25 000, 1:50 000, 1:100 000
• Proprietory maps of various scales
Melways – eg Metropolitan Melbourne
Spatial Vision map books – Vic country
Cadastral maps
EIMS mapping
Hand drawn mapsDEPI Fire map
Vicroads map – 1:250 000
Aviation charts
Marine charts
Specialist maps
• Land use
• Fire history
• Fire intensity
• Topographical
• Cadastral map
• Spatial Vision Central
Map book, Map 6524
– 1:20 000 (purple) towns
– 1: 50 000 (blue) rural
– 1:15 000 (beige/orange)
regional city
– 1:100 000 (yellow)
rural/remote
• DEPI Fire Map
• Melways – Bayswater
• Fire Hazard
mapping
– Degree of
hazard map
E.g. based on
distance from the
native vegetation (or
could be distance
inland for a tsunami
hazard map)
• Hazard Class
Mapping
– Every area given
a class to fit into,
and themed
appropriately
– E.g. types of
vegetation
• Incident
Management
System (IMS)
– This map
shows wind
direction and
speed
Map Symbols
The legend at the bottom or side of a map provides
a listing and explanation of symbols used on that
sheet.
Symbols are used to
• Define features which exist on the ground
• Draw your attention to features which may not be
recognised if they were drawn to scale and shape.
For example, a building would appear as a speck
on a map with a scale of 1:100 000
• Highlight features such as administrative
boundaries and areas of responsibility.
The addition of colour makes it easier for you to
identify other features
15
As part of an international standard:
blue is used for water features,
black for man-made (Cultural) features,
green for vegetation types,
brown for relief,
red-brown for road classifications,.
16
Marginal Information
17
18
19
20
21
22
23
Marginal Information
25
26
Scale
Converting Units of Length
100 cm = 1 metre
1000 m = 1 kilometre
Or 100 000 cm = 1 kilometre
If the scale is 1:100 000 (1 cm = 100 000cm) then 1 cm on the map = 1
km on the ground
• Every one unit of measurement on the map equals 100 000 units on the
ground
• large scale ideal for road maps etc
• 1:100 000 accurate to 100m only limited detail
smaller scales
• 1:50 000 - 1cm on map equals 500m on the ground
• 1.25 000 – 1cm on map equals 250m on the ground
•
The smaller the scale the more detail can be displayed
28
29
30
Ground Shape
– Topographical maps show us the shape of the
ground
•
•
•
•
•
•
•
Contour line – a line that joins points of equal elevation
Ridgeline – line along the top of a hill or a mountain
Aspect – the compass direction that a slope faces
Crest – the highest part of a hill or a mountain range
Gorge – a deep ravine (a valley with steep sides)
Knoll (knob) – a low, detached hill
Spur – minor feature, normally in the form of a ridge running out from a hill
or a mountain
• Plateau – elevated area which is flat
• Undulating ground – ground that rises and falls gently
There are many ways to represent relief on a
map, including:
• Hachures
• Hill Shading
• Hypsometric Tinting
• Contour Lines
32
Hachures
Hachures are an impression of the shape of the ground, but
as they do not display exact information regarding height,
slope and height cannot be measured. Hachure lines also
tend to obscure other details on the map
33
Hill shading
A map with hill shading is drawn as though there is a very
bright light shining on the area normally from the northwest. This light creates ‘shadows’ in the deep valleys and on
the mountains. These shadows will show up the shape of
the mountains, but not their height. Hill shading may be
found on some larger scale maps such as the 1:250 000
series.
34
Hypsometric tinting
Hypsometric tinting in atlases and on some maps uses
different colours (or shades of a colour) to show differences
in the height of the land.
35
Contour lines
The height of a feature or location is referred to as its
elevation, and is measured as being above the Australian
height datum (mean sea level).
Contour lines connect points of equal elevation. With
careful interpretation, they provide an indication of the
height and ground shape of an area. The distance separating
these lines is known as the vertical interval (contour
interval) and is indicated in the marginal information
section of a map. Contour lines are drawn in orange/brown,
and every fifth or tenth contour line may be drawn more
heavily to make it easier to identify height. Some contours
have their elevation shown along their length.
36
37
What do contour lines show?
From the contour lines, you should be able to calculate the height of the
land.
However, it is not so easy to picture the shape and slope of the land,
unless you understand the patterns made by these lines.
Every topographical feature is represented by its own unique contour
pattern. In order to read the patterns you must remember:
1) If the contour lines, reading from high to low, increase, then the
slope is concave.
2) If the spacing of the contour lines, reading from high to low,
decreases, then the slope is convex.
3) Evenly spaced contour lines indicate a steady slope.
4) Widely spaced contour lines indicate a gentle slope.
5) Contour lines which are close together indicate steep slopes.
38
Contour Lines
Contours are lines drawn on a map connecting
points of equal height above sea level
39
• Contour heights
41
Topographical features
43
44
Representation of height
Elevation may also be shown in black figures on a
map.These figures have different levels of accuracy:
Elevations of “Trig stations” are shown in figures
beside a solid black triangle. These heights are
precisely surveyed.
The elevation of points determined by other survey
methods are indicated beside a circle or a triangle
Spot heights are estimated from contours they are
indicated by a number beside a dot (for example • 254).
This indicates the approximate height at that point.
The type and origin of elevation symbols used on a
particular map sheet are usually explained in the map
legend
45
Calculating slope (gradient)
The slope of the ground, the angle the ground surface
makes with the horizontal, is normally expressed as a
gradient.
A gradient of 1:10 means that in a horizontal distance of 10
units, the ground rises or falls 1 unit.
To determine whether there is safe access up or down a slope.
Contour lines give you an indication of how steep the land is
in a particular area, but you will obtain a clearer picture of the
steepness of an area by either:
• measuring the angle of slope in the field, or
• calculating the steepness of a slope from a map
46
Measuring the angle of a slope in the
field
A clinometer is an instrument used to measure the angle of a slope.
When you look up a slope through the sight tube, the indicator needle on
the scale swings backwards from the zero mark. This indicates the
angle of the uphill slope. When looking down a slope, the needle will
fall forwards and indicate the angle of a downhill slope.
If you don’t have a clinometer, you can construct one from a drinking
straw, paper clip and cardboard.
47
Measuring the angle of a slope in the
field
48
Calculating the steepness of a slope
from a map
When it is necessary to calculate the steepness of a slope
from a map, you measure the horizontal distance between
two successive contour lines, and express this in the same
unit as the contour interval.
For example, if the contour interval is 10 metres, and the
horizontal distance between contour lines as measured
from the map is 200metres, the average gradient is
10/200 = 1:20.
vertical distance
10
1
Gradient = horizontal distance = 200 = 20 = 1:20
49
When you need to express slope in degrees, it is essential
that both the vertical distance and horizontal distance are
converted to the same units of measurement, and a scale
drawing produced. The slope is then simply measured
with a protractor.
For example: Vertical distance of 250metres.
Horizontal distance of 1000metres
50
As most slopes vary in steepness at different points on
them, your calculation will only provide you with an
average gradient of the slope.
People have a tendency to overestimate slope, so when you
are looking down a slope of 1:3 or 1:4, you may be
convinced that it is no less than 1:1.
To ensure safe travel to an incident, it is important to
continually visualise the slope by reference to the map.
51
Maximum gradient for safe vehicular use
As a general rule, for safe vehicular use, the gradient of a
road or track should not be steeper than a ratio of 1:6,
except for very short distances. It should never exceed 1:3.
52
Intervisibility (line of sight)
It may be necessary to determine what area of ground you
can view from a particular location.
You can say that two places or features are intervisible if
one can be seen from the other. If you cannot see one
feature from the other, then you can say that the place
which cannot be seen is in ‘dead ground’.
Two places will not be intervisible if there is an area of
higher land between them.
53
Obstructions
You can establish line of sight by carefully examining a map.
It will show if there is higher ground between the
observation point and the object being considered.
Other obstructions, such as trees must also be taken into
consideration, and allowance made for their height. This
additional height is not usually indicated on a map.
54
55
In order to get a clearer picture, you may need to make a
‘section’ of the line of sight, as follows:
1.
Draw a line on the map between the two points (A and B)
2. Lay a straight piece of paper along the line AB and mark it at points A
and B. Then mark the points at which each contour cuts this line. Label each
point with it’s elevation and consider additional height allowances for
obstructions.
3. At each mark, drop lines on the paper perpendicular to the marked edge.
Parallel to the marked edge draw a series of parallel lines to a convenient
scale to represent the elevation of each of the contours cut by the line AB.
4. Make a mark where each vertical line intersects the corresponding
elevation line, parallel to the height shown on the line AB. Join these marks
with a smooth line
5. The slopes will appear to be exaggerated depending on the ratio of the
map scale to the vertical height scale selected, but otherwise, the section will
give an accurate representation of the surface of the ground
56along the line
AB. This will show the line of sight.
57
• North Points
– True North
• The axis on which the earth spins, which passes
through the North Pole
– Magnetic North
• The direction in which a magnetic compass
points, which changes every year
– Grid North
• The direction of the eastings grid of a map
Measuring distances
Ways of measuring distances on maps
• Transfer distance to scale using
– String
– Ruler
– Paper
Measuring a straight distance
Measuring a curved distance
Map orientation
A map is said to be ‘set’ or ‘oriented’ when it has been
turned around so that the features on the map are in the
same relative position as the features on the ground. This
can be achieved in two ways:
a) Setting by inspection- You select significant features
you can see on the ground that are easily identifiable on
the map. The map is then rotated so that the features on
the map are lined up with those on the ground.
b) Setting by compass- The compass is placed on the map
over the magnetic variation diagram with the compass index
line (axis) along the magnetic north line of the diagram. The
map is rotated until the north point of the compass needle
points directly along the index line of the compass.
63
Fixing a position
There will be occasions to accurately locate on the
ground an object that has been identified earlier on a
map. Or you may need to determine your own position.
This can be done in three ways:
1) Using local objects
2) By triangulation
3) Using resection, or back bearings.
64
Using local objects
Before attempting to find a position on the map, you
must first set the map.
You then compare the detail from the map with the
ground. This will enable you to determine your
approximate position. Increased accuracy can be obtained
when you relate that position to more detailed features,
such as creeks or houses.
Natural features are more reliable than man-made
features as the latter are sometimes relocated. For
example roads can be re-aligned, or fences moved.
65
Using local objects
66
Finding your way without a compass
or map
By day, with the sun visible
When you point the 12 position on your analogue watch
towards the sun, true north is located approximately half
way between that position and the hour hand.
67
What to do when lost
If you suspect that you are lost, stop and consider:
• Have you already passed the objective, and was the time
and distance traveled badly estimated?
• Have you wandered away from the bearing line ?
• Does the ground conform with the mental picture formed in
studying the map in the planning phase?
• Are there any ground features which will help you to
determine your position?
• Is there a possibility of compass error, local magnetic
attraction due to geological features, or map inaccuracy?
68
Fixing of position
When you review the factors above, you can often
reduce your current ‘lost’ position to two or three
probable locations.
A brief reconnaissance in opposite directions will usually
provide additional information to allow you to finally fix
your position.
•If in doubt, STAY WHERE YOU ARE and await rescue
69
Fire behaviour
70
Weather
The four key elements of weather are air temperature, relative
humidity (the percentage of moisture in the air), wind speed
and direction, and atmospheric stability.
Air temperature
Changes in air temperature will affect the behaviour of a fire or
hazardous materials incident. Air temperature decreases with
elevation, so the rate of spread of a fire, or the volatility of a
gas escape, at higher elevations is usually reduced. Elevation
can be interpreted from a map.
71
Relative humidity
The moisture content of the ‘dead’ component of fuel varies
directly with relative humidity.
High RH may also make it more difficult to disperse
hazardous gases and vapours from the vicinity of an incident.
However, no information about RH which would be of
practical value to emergency responders can be interpreted
from maps.
72
Wind speed and direction
The greater the wind speed, the faster a wildfire will
spread. Wind speed will be higher on hill slopes
exposed to the wind and less on sheltered slopes.
This information can be interpreted from maps.
Wind direction is affected by the shape of the ground.
Exposed faces of hills and ridges can create an
interaction with the wind. Increased wind speeds near
the ridge can often lead to almost calm conditions on the
leeside.
This can be interpreted from maps. Each locality has its
characteristic winds.
73
Topography
The effect of topography on wind is most evident
in mountain valleys and gullies. The position of
these can be interpreted from topographical maps.
An increase in wind strength may take place when
the wind is confined by the sides of a valley.
When the terrain is rough, turbulence can be
created, particularly near the intersections of the
main valley and side gullies.
Aspect and slope can also affect incident
behaviour. Both features may be interpreted from
topographical maps.
74
Aspect
Aspect is the direction that a feature or slope faces.
Northerly and Westerly aspects, with exposure to the
greatest amounts of solar radiation, are usually drier
and warmer, and this influences the nature of
vegetation growing there.
Fires on these aspectes will generally burn more
intensely than fires on southern and eastern aspects.
In south-western Australia, fuels on exposed east or
north-east aspects become dry, and may support fast
moving intense fires.
75
Slope
The effect of slope on a fire is to change the flames to a
more acute angle. This accelerates the drying and
preheating of the fuel and thus increases the rate of spread
of a wildfire.
Fire speed on a 10º slope is double that of a fire on level
ground, and the speed increases almost four-fold when
the fire travels up a 20º slope.
Conversely, the fires speed decreases on down slopes.
76
• Fires on slopes spread faster uphill. Fire speed on a
10% slope is double that of a fire on level ground and
increases almost four-fold travelling up a 20%.
• Fires on slopes with northerly or westerly aspects will
generally burn more intensely.
• Rough topography can cause wind turbulence on the lee
side of a hill.
• Valleys and gullies will channel and strengthen winds,
and can cause rapid changes in incident behaviour.
77
Cold Fronts, Wind Changes and Fire
Behaviour
• Cold fronts, or changes, have a major
impact on fire behaviour:
– Strong, gusty, hot and dry north to northwesterly winds prior to the change promote
fast moving intense fires
– Lighting may ignite new fires
– It might be a dry change i.e. precipitation is not
expected
– The west to south-westerly wind change may
turn the east flank of the fire into the main fire
78
front
Effect of a Wind Change on Fire
Behaviour
79
• Selecting the best route
– Factors on determining the best route
•
•
•
•
•
•
•
•
•
•
•
•
•
Condition of roads
Time of year
Time of day
Degree of slope
Bridges and river crossings
Shape of ground
Gullies and ravines
Other traffic
Type of vehicle driven
Experience of driver
Local knowledge
Turn around points
Extrication equipment
• Map Grid
Australia –
– UTM Zones
(Universal
Transverse
Mercator)
• Map references:
– There are many ways of mapping the world. In
Australia, the projection that fits the best is the
Universal Transverse Mercator Projection.
– Using this, every point in the world has a unique 16
digit reference, which is made up of
• A 2 digit figure and a letter referring to the zone
• A 2 figure number, which is known as the easting
• A 7 figure number, which is known as the northing
– A UTM is displayed as follows: 55H 234319 5819346
• Gaining a six figure reference from a UTM:
– Delete the zone reference
– Delete the 1st, 5th, and 6th figures of the easting
– Delete the 1st, 2nd, 6th and 7th figures of the northing
• 55H 2 343 19
58 193 46
• Eastings /
Northings
– In the door and up
the stairs
• Grid Squares
– Establish what the
scale is, and how
much area each
square encompasses
– E.g. for a 1:100 000
scale map, each
square is 1km2
• Be aware of different map datums (a model for
the surface of the earth)
– GDA 94
– AUS 66
– WGS 84
• Why are they different?
– They use a different approximation for the shape of the earth,
and usually optimised for use in one particular part of the world
– Can create minor differences (up to 120m) in projection
• Where would you find this information? In the legend
• When reporting a reference, the information
required is
– Name of map being used
– Edition of map
– Page or map number (if appropriate)
– Datum of map
– Map reference of locality
• Eastings and northings
• Reporting and identifying locations e.g.
– Hotham 1:50 000 Grid Ref 123 678
– VicMap Raywood South 7724-4-S 1:25000 Grid Ref 375 382