Geography 2122A/B Chapter Notes - Chapter 13: Laser Rangefinder, Binoculars, Centimorgan

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Published on 16 Apr 2013
School
Western University
Department
Geography
Course
Geography 2122A/B
Professor
Chapter 13
Position Finding and Navigation
Orienting the Map
Orient a map means to determine how directions on the map align to
directions on the ground.
Before maps were drawn with China on Top, but now made using True North
at the top
Inspection Method
o Easiest ways to orient map inspection method
o With this technique, do not need to know which way north is.
o No need of tools. Only 2 conditions need to be met:
Must be able to see one or more linear features or prominent
objects in your vicinity
Must be able to identify the same features on the map
o One Linea Feature
Position yourself on a linear feature shown on the map, such as
a road
Then turn the map until mapped feature lines up with the real
on in front of you.
The line you see between you and the features is called sight
line.
2nd method is to assume a position that lies on a straight-line
extension of the ground feature.
3rd option is to take up a position to either side of the linear
ground feature and then to align the feature shown on the map
so that it is parallel with the ground feature.
1st and 3rd have problems.
o Two linear features (better option than one linear feature)
3 options:
1st more to position on either of the two linear features,
2nd move to a point which lies on a straight line extension of
either feature
3rd or assume a position off to one side of both features.
Turn the map until 2 features align with those on ground
3rd is the least accurate
o Prominent Features
Reversal in map orientation can be avoided by using 2 features
to align yourself.
Move to one feature, or to a position on a line extended
through the two features.
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If you are located off to the side of the features, estimate your
position relative to the straightedge line between the
prominent features.
Identify ground features that can be found on the map. =
success!
o Compass Method
Firstly, need compass, a map showing magnetic north with
declination diagram.
Then do this:
Find magnetic north indicator on map
Hold map under compass, turn map until compass
needle lines up with magnetic north on the map
This will orient with true north as well.
Essential to take magnetic declination because true north is a
bit off.
Magnetic north isn’t always shown on maps
Commit the basic declination pattern to memory.
Finding Your Ground Position
Distance Estimation
o Most common technique
o In which you use your distance and direction to other objects to
location your position on the map.
o Two useful methods: by inspection and using a compass
o Inspection Method
Looking at ground features without any special aids. Find
ground features you find on map with ground and estimate
their distance from you
First, orient your map and select a feature on the ground that
you can also identify on the map
Second, estimate the distance from your ground position to the
distant feature, and convert this figure to map distance unites
by using the map scale.
Mark out the computed map distance along the proper
direction line and you have established your position
A further complication is that farther distances are easier to
estimate than nearer distances.
As you approach vanishing point (point on horizon where
parallel lines appear to converge), it becomes harder to judge
distance.
o Compass Method
Distance estimation using map and a magnetic compass,
which indicates directions magnetically buy the alignment of a
magnetic needle or floating disk to the earth’s magnetic field.
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Document Summary

Orient a map means to determine how directions on the map align to directions on the ground. Before maps were drawn with china on top, but now made using true north at the top. Inspection method: easiest ways to orient map inspection method, with this technique, do not need to know which way north is, no need of tools. Must be able to see one or more linear features or prominent objects in your vicinity. Must be able to identify the same features on the map: one linea feature. Position yourself on a linear feature shown on the map, such as a road. Then turn the map until mapped feature lines up with the real on in front of you. The line you see between you and the features is called sight line. 2nd method is to assume a position that lies on a straight-line extension of the ground feature.

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