# 4.2 Magnetic north map skills

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## Magnetic north map skills

You became acquainted with basic map skills in Grade 8 and did exercises that involved the 1:50 000 topographic map of Alice. In doing that, you learned to:

determine location

gauge accurately and determine direction

calculate distance by making use of a scale

explain the naming of a map

recognise conventional map symbols

recognise representation of height on maps

identify contour patterns

This knowledge, together with what you will still be acquiring in using the 1:50 000 topographic map of Bloemfontein and a 1:10 000 orthophoto map of a portion of this will see you through this year’s work.

Before commencing the practical exercises, you have to learn a number of additional map skills.

Calculating distance on an orthophoto map.

Orthophoto maps are always drawn to the scale of 1:10 000. Follow the steps to determine distance:

Accurately measure the distance between two points in centimetres, using a ruler (or using a string if the line to be measured curves);

Convert this distance to kilometres or metres, depending on what is required.

Example

A________________________________B

The length between A and B is 10 cm.

Scale 1 1:10 000

What is the true distance in km?

10 cm x 10 000

100 000 cm ÷ 100 000

1 km

What is the true distance in m?

10 cm x 10 000

100 000 ÷ 100

1000 m

Why do we divide by 100 000 and 100?

The metrical units of measurement can be represented as follows:

 Km Hm Dm M dm cm mm 1 0 0 0 0 0 1 0 0

We therefore have 100 000 cm in 1 km

and

100 cm in 1 meter

You may therefore follow the shorter method if you can remember that the scale of

1 : 10 000 is the same as:

1 cm = 10 000 cm

1 cm = 100 m (÷ 100)

1 cm = 0,1 km (÷ 100 000)

## Activity 1: [lo 1.3]

1. Calculate the true distance in metres if the distance on a 1:10 000 orthophoto map is as follows;
1. 5,8 cm.
2. 10,1 cm.
3. Calculate the true distance in kilometres if the distance on a 1:10 000 orthophoto map is as follows;
1. 92,2 cm.
2. 15,6 cm. Magnetic North and Magnetic Declination

You have learnt how to gauge accurately in Grade 8. Remember the steps that have to be followed:

Connect the two points by means of a pencilled line.

• Draw a line to show True North through the point FROM which you have to measure.
• Position the protractor by placing 0° against the line indicating north and the centre at the point from which the measurement is to be taken.
• Measure the angle clockwise from the line for north to the connecting line (pencilled line of Step 1.)

Example:

On a map, North therefore indicates the North Pole, which we refer to as TRUE NORTH (geographic north.)

The earth also has a magnetic field that extends from north to south, for which we use a compass. The earth’s magnetic field does not correspond exactly with the true North and South Poles. North as indicated by the compass will always lie WEST of TRUE NORTH (TN) and is known as MAGNETIC NORTH (MN).

The difference between true north and magnetic north is known as the MAGNETIC DECLINATION (MD). The Magnetic Declination differs from place to place and continuously increases and decreases at any place, because magnetic north is not a fixed point.

To make it possible to determine the Magnetic Declination of any place, the following information is given in the margin of a 1:50 000 topographic map:

Example:

Calculate magnetic declination as at present:

Step 1:

Calculate the difference in years = 2003 – 2000

= 3 years

Step 2:

Multiply the years by the annual difference in minutes = 3 years x 4'

= 12'

Step 3:

Determine whether the angle increases (eastwards) or decreases (westwards).

Eastwards (smaller) -

Westwards (bigger) +

Step 4:

Add the minutes (westwards) or subtract them (eastwards).

In this instance it is eastwards, therefore:

21°30' - 12'

= 21°18' West of True North

REMEMBER that there are 60' in 1°.

If you should have to subtract and find that the degrees to be subtracted are too many, you “borrow” 1° and convert it to minutes.

Example:

21°30' – 34'

20°90' - 34'

= 20°56' West of True North.

If you should have to add minutes and get an answer that is more than 60’, you have to convert it 1°.

Example:

21°30' + 34'

21°64'

= 22°04' West of True North.

Step 5:

Remember to write West of True North alongside the new declination, because Magnetic North ALWAYS lies WEST of True NORTH.

Magnetic North

To gauge Magnetic North between two points, the degrees of TRUE NORTH must be added (+) to the Magnetic Declination and the answer must be written in degrees:

Example:

TN + MD = MN

50° + 21°18' = 71°18'

## Assessment

 Learning Outcomes(LOs) LO 1 Geographical EnquiryThe learner will be able to use enquiry skills to investigate geographical and environmental concepts and processes. Assessment Standards(ASs) We know this when the learner: 1.2 asks questions that are relevant for identifying sources; 1.3 draws conclusions and makes analyses to obtain information from sources such as photographs, maps, atlases, graphs and statistics; 1.4 correlates information from different sources; 1.7 reports on knowledge that they have obtained through research, making use of different sources of information. LO 2 Geographical Knowledge and UnderstandingThe learner will be able to demonstrate geographical and environmental knowledge and understanding. We know this when the learner: 2.2 identifies ways in which Science and Technology have contributed a positively and negatively influence to development (people and resources.)

## Memorandum

ACTIVITY1:

• 580 m
• 1 010 m
• 9,22 km
• 1,56 km

ACTIVITY2:

1. True North / Bearing :

Magnetic Declination:

1990 – 2003 = 13 years

13 × 2’ = 26’ westwards

18 0 41’ + 26’ (westwards)

= 18 0 67’

= 19 0 07 west of true north

Magnetic Bearing: WN + MD = MN

…… + 19 0 07 = ………………………..

1. Actual Bearing :

Magnetic Declination: 1993 – 2003 = 10 years

10 × 3’ = 30’ eastwards (-)

20 0 15’ – 30’

19 0 75 – 30

= 19 0 45’ west of true north

Magnetic Bearing: WN + MO = MN

...................... + 19 0 45 =..................................

#### Questions & Answers

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nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
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There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
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da
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Bhagvanji
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Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
revolt
da
Application of nanotechnology in medicine
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ya I also want to know the raman spectra
Bhagvanji
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please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
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Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
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Alexandre
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Rafiq
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Damian
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What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
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Santosh
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Rafiq
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Mahi
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Rafiq
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Anam
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Anam
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Hafiz
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Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
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Renato
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?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
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