Comprehensive Notes on Mapwork Skills, Topographic Maps, Aerial Photography, GIS, Atlases, and Fieldwork

Chapter 1: Mapwork Skills

• Key question: How to describe exactly and easily where a place is on the surface of the Earth.
• The chapter will cover mapwork skills and techniques applicable to both smaller scale maps in atlases and larger scale 1:50 000 topographic maps.

Unit 1: Locating Exact Position

1.1 Locating Exact Position in Degrees and Minutes

• Co-ordinates help locate a place quickly and easily on a map. Co-ordinates are two reference numbers that give the exact position of a point on a map or graph.
• On atlas maps, co-ordinates are given in degrees and minutes.
• Example: Port Alfred is located at $33°36'S; 26°54'E$.
• Key points to remember:
  • There are 60 minutes (60') in one degree (1°) of latitude and longitude.
  • Latitude is the angular distance south (or north) of the equator.
  • Longitude is the angular distance east (or west) of the prime (Greenwich) meridian.
  • Latitude is stated first, followed by longitude.
  • Always include S (for South) or N (for North) with latitude and E (for East) or W (for West) with longitude.
• Locating Port Alfred quickly:
  • $33°36'S$ will be just over halfway between $33°$ and $34°S$.
  • $26°54'E$ will be very close to $27°E$.

1.2 Locating Exact Position in Degrees, Minutes, and Seconds

• Large-scale maps provide finer detail, requiring the use of seconds to define exact locations.
• There are 60 seconds (") in a minute (').
• To find the co-ordinate position:
  1. Project latitude and longitude to the grid markings on the edge of the map.
  2. Read the latitude and longitude co-ordinates, estimating between marked values if necessary.
  3. Example: Knysna railway station is at $34°02'25"S; 23°02'38"E$.
• Using a Romer card (minute-divider) increases accuracy and saves time:
  • A Romer card is a small rectangular piece of paper the exact size of one minute each way.
  • Divide the edges into 10-second intervals (or even 5-minute intervals).
  • Place the Romer card on the map with the bottom right corner at the point to be located.
  • Read off the seconds where the Romer card crosses a minute line.

1.3 Locating an Area

• To give the exact position of an area, name the whole minute square it is in.
• Locate the square by giving the co-ordinates of its top left corner.
• Example: Most of Thesen's Island is in minute square $34°02'S; 23°03'E$.

Unit 2: Relative Position: Direction and Bearing (True and Magnetic)

• Direction and bearing describe where one place or point is in relation to another.

2.1 Direction

• Direction is given using compass points like north, southeast, and west-northwest.

2.2 Bearing

• Bearing is measured in degrees from $0°$ to $360°$, starting from true north ($0°$) and increasing clockwise.
• To measure true bearing on a map:
  1. Draw an accurate north-south line through the starting point (e.g., Brenton railway siding), ensuring it is parallel to the map's edge.
  2. Draw a line from the starting point to the target (e.g., trigonometrical beacon 262).
  3. Place a protractor on the north-south line with its centre over the starting point and $0°$ and $180°$ points on the north-south line.
  4. Read the bearing in degrees.
• Useful tips:
  • State bearing simply as a degree, without adding 'W' or 'E'.
  • Use a full circular protractor ($0°$ to $360°$) for faster and more accurate measurements.

Finding Magnetic Bearing

• Magnetic compasses point toward the magnetic north pole, not true north.
• In 2010, the magnetic north pole was at $85.1°N; 133.0°W$.
• Magnetic declination is the angle between true north and magnetic north.
• In Knysna, the magnetic declination is about $27°$ west of true north, so magnetic bearings are about $27°$ greater than true bearings.
• Key points:
  • A magnetic compass in Knysna will point about $26°46'$ to the west of true north.
  • Magnetic declination increases westwards every year as the magnetic north pole 'wanders'.
  • In South Africa, magnetic declination must always be added to the bearing.
  • Magnetic declination is always indicated on topographic maps.

Unit 3: Scale and Distance

• Maps are drawn to scale to represent ground space, always smaller than the area they represent.
• Scale is the proportion which the length between any two points on a map bears to the horizontal distance between the same two points on the ground.

3.1 Scale

• Three ways of stating a map's scale:
  1. A word statement (e.g., '1 cm represents 1 km'). In Figure 1.1, 1 cm represents 25 kilometers. In Figure 1.4, 1 centimeter represents 500 meters (and 2 centimeters represent 1 kilometer).
  2. A ratio (e.g., 1:50 000) is the proportion between a length on a map and the corresponding length on the ground. The ratio scale is 1:50 000 on the map in Figures 1.4 and 1.21. This means that 1 centimetre on the map represents 50 000 centimetres on the ground.
     $1 cm : 50 000 cm$
     $1 cm : 500 m$ (Divide by 100 because there are 100 cm in 1 m)
     $1 cm : 0.5 km$ (Divide by 1000 because there are 1 000 m in 1 km)
  • A ratio scale is always given with the first number as 1.
  • Sometimes a map ratio is expressed as a representative fraction, such as $\frac{1}{50,000}$.
  1. A line scale is a long line, accurately divided, which allows a user to make direct measurements on a map using dividers or a strip of paper. All good maps have a line scale so it is not necessary to calculate distances.
• Scale is the proportion which the length between any two points on a map bears to the horizontal distance between the same two points on the ground.

3.2 Measuring Straight-Line Distances on a Map

• Two methods: using the line scale and converting map distances to ground distances.
• Using the line scale:
  • Mark the distance between two places on the edge of a piece of paper.
  • Lay the edge of the paper on the line scale to find the ground distance.
• Converting map distances to ground distances:
  • Use calculations only if the map has only a ratio scale.
  • Measure the map distance with a ruler.
  • Example for a 1:50 000 map: If the map distance between two points is 7.4 cm, then:
    $7.4 cm : 7.4 \times 50,000 cm$
    $: 370,000 cm$
    $: 3,700 m$ (Divide by 100 because there are 100 centimetres in 1 metre.)
    $: 3.7 km$ (Divide by 1000 because there are 1 000 metres in 1 kilometre.)

3.3 Measuring Route Distances Along Curved and Irregular Lines

• Use a strip of paper to find distances along irregular lines (roads, rivers, shores):
  1. Lay a strip of paper along the line.
  2. Mark on the paper wherever the paper edge leaves the line.
  3. With a sharp pencil point as a pivot, swing the edge back onto the line.
  4. Repeat the process until you reach the end of the line.
  5. Use either a line scale or a calculation to convert map distance to ground distance.

Unit 4: Calculating Area

4.1 Calculating Areas on Atlas Maps

• Example: Finding the areas of Lesotho and Eswatini.
  1. Draw straight lines along the edges of the countries to enclose each of them in a rectangle.
  2. Of each country leave out the same amount of area as you 'wrongly' included in the rectangle.
  3. On a strip of paper, mark the length of each side of the rectangle.
  4. Carefully use the line scale to find the average length and width of each country (in km).
  5. Multiply the length (in km) by the width (in km) of each country to find the area (in km²).
• For very irregular map areas, use more than one rectangle or even triangles.
• Calculation examples:
  • Lesotho (Area = 210 km x 145 km = 30,450 km²). Actual land area is 30 450 km² with an error of only 0.3%.
  • Eswatini (Area = 160 km x 110 km = 17,600 km²). Actual land area is 17 360 km² with an error of 1.4%.

4.2 Calculating Areas on the 1:50 000 Topographic Map

• Method 1: Finding the area of a rectangular field or farm.
  • Measure the length and width of the area (in metres or kilometres) and multiply these to find the land area in square metres (or square kilometres (km²).
• Method 2: A quick way to calculate areas on a 1:50 000 topographic map.
  1. With a sharp pencil trace Figure 1.13.
  2. Lay it over the map area of which you want to estimate the size. If the area is large, you may need to make more than one area estimate and add these together.
  3. You can also use graph paper with 2 mm squares. Every 2 mm square represents 1 ha (or $\frac{1}{100}$ km²). Every 2 cm square represents 100 ha (or 1 km²).
  4. Count all the 2 mm squares in the area. (Ignore areas that are less than half a square, but count areas that cover more than half a square.)
  5. The only calculation that you need to do is to divide the total number of small squares by 100 to find the area in square kilometres.

Chapter 2: 1:50 000 Topographic Maps

• Topographic map shows the surface features of an area to scale, including physical features (relief and drainage) and human features (settlements and communications).
• The 1:50 000 topographic maps are the largest-scale maps that cover all of South Africa, requiring 1913 large map sheets.
• Symbols are used to represent:
  • Physical features: relief (the shape of the land, for example hills, valleys, cliffs) and drainage (streams, rivers, lakes, marshes).
  • Woodland (natural forests and plantation forests).
  • Human features (buildings, farmland, railways).
  • Boundaries and place names.

Unit 5: Contours and Landforms

• 1:50 000 topographic maps provide information about the altitude of objects.
• Ways of reading altitude:
  1. Trigonometrical station.
  2. Spot height.
  3. Bench mark.
  4. Contours.
• A contour is a line drawn on a map joining points which are the same height above sea level. They indicate heights in metres and appear as brown lines on a topographic map. The numbers always face down the slope.
• A contour interval is the difference in height between two consecutive contours. On 1:50 000 topographic maps, the contour interval is 20 m. Every 100 m contour is a thicker line.

5.1 Using Contours to Identify Landforms

• Compare the map with a computer model of the landscape to understand how ridges, hills, cliffs, and valleys are shown.
• Key landform features:
  • Gentle slope: Contours are fairly widely spaced.
  • River valley: Evenly spaced contours on both sides of the valley indicate a V-shaped cross section. The contours point up the valley.
  • Flat coastal plain: No contours, meaning the area is below 20 m msl.
  • Cliff: Very steep slope with contours that are very closely spaced and may even touch.
  • Concave slope: Flat land curving upwards, with flatter lower parts and increasingly steep higher slopes.
  • Spurs and valleys: Spurs are narrow ridges tapering down at the tips, with shallow valleys between them.
  • Coastal sand dunes: Long, thin loops (like sausages).
  • Asymmetrical ridge: Unevenly steep slopes on either side of the ridge.
  • Flat island: No contours, indicating it does not rise above 20 m msl.

Unit 6: Cross Sections on 1:50 000 Topographic Maps

• Cross sections provide a better understanding of a landscape by showing a downward 'slice' through it.
• They are used to:
  • Get a clearer idea of the landscape.
  • Show how slopes change.
  • Identify landforms.
• Steps to draw a cross-section:
  1. Collect height data from the map by laying a strip of paper on the section line and marking where the contours occur. Note the heights of each contour on the strip and also indicate any valleys and ridges.
  2. Prepare a grid with grid lines for all the altitudes crossed by the section line. Transfer the data to the grid.
  • Join the height marks with a smooth pencil line.
  • Label the end points of the cross section.
  • Shade the solid part of the cross section.
  • Add a title saying what the cross section shows.
  • Add the horizontal scale and the vertical scale.
  • Add the vertical exaggeration of the cross section.
• Interpolation is the insertion of a value between known or measured values.
• Extrapolation is finding a value beyond known values

Unit 7: Vertical Exaggeration and Intervisibility

7.1 Vertical Exaggeration

• Hills and mountains are made to look higher than they are in comparison with their width.
• Cross sections usually have the same horizontal scale as the one used on the map. The vertical scale is often larger than the horizontal scale to show up hills, mountains and valleys more clearly.
• Vertical exaggeration (VE) is the extent to which vertical distances on a cross section have been increased compared with the horizontal distances. Without VE, hills and mountains would look too flat.
• Cross sections drawn from a 1:50 000 topographic map usually have a vertical exaggeration of between 5 and 10 times.
• Formula for finding VE:
  $VE = \frac{vertical scale (as a fraction)}{horizontal scale (as a fraction)}$
• Route profile is a cross section where the section line follows the road rather than a straight section line.

7.2 Intervisibility

• Two places that can be seen from each other are said to be intervisible.
• Cross sections can be used to find intervisibility.
• Knowing intervisibility is important:
  • When choosing a site to build a house with a view.
  • In selecting a site for a security or military lookout.
  • In locating sources of light signals and some types of radio signals.
  • When building radio receivers (like radio telescopes) that need to be cut off from light and radio signals.
• Cross sections used to find intervisibility does not take woodland, rows of trees or buildings that may block the view into account.

Unit 8: Gradient

• Gradient is the steepness of land slopes.
• Slope is important: gently sloping land is needed for building, farming, roads, and railways that cannot be built up or down steep slopes.

8.1 Use a Gradient Scale

• Lay the edge of strip of paper through the middle of the trigonometrical station and running at right angles to the contours.
• On the strip mark the eight contour lines and label them with their heights.
• Match the contour marks with the contour spacings in Figure 1.34 to estimate gradient. Example gradient of 1:2 means a person walking up this slope will rise by 1 metre for every 2 metres he/she goes forward.

8.2 Calculate the Gradient of a Slope

1. Measure the horizontal distance from the trigonometrical beacon to the 100 m contour below it (Use line scale method).
2. Find the vertical difference between the 100 m contour and the trigonometrical beacon.
3. Draw a sketch to show these two measurements.
4. Calculate the average gradient of this slope.

• Formula:
  $Gradient = \frac{vertical rise}{horizontal distance}$
• Remember as 'up' over 'along'.

Chapter 3: Aerial Photographs and Orthophoto Maps

Unit 9: Using Oblique and Vertical Aerial Photographs to Identify Ground Features

• Aerial photographs are taken from aircraft flying overhead.
• Types of photographs:
  • Oblique aerial photograph (Figure 1.17) where the camera has an angle from horizontal.
  • Vertical aerial photograph (Figure 1.22) where the camera is pointing directly down.

Low Oblique

• Angle from vertical: $5°$ to $45°$.
• Horizon visible: No.
• Ground area shown: Distorted.
• Scale: Decreases a little toward background.

High Oblique

• Angle from vertical: $85°$ to $45°$.
• Horizon visible: Yes.
• Ground area shown: Distorted.
• Scale: Decreases with distance.

Vertical

• Angle from vertical: $0°$.
• Horizon visible: No.
• Ground area shown: True.
• Scale: Same over the whole area.

Unit 10: Interpreting Vertical Aerial Photographs

• Large scale vertical photographs show great detail and are used to interpret what aerial photographs show by looking for clues from the visual elements.

Visual Elements:

1. Tone: Lighter tones suggest sand, ripe crops, or concrete. Darker tones suggest forest or freshly ploughed farmland. Sunlight reflection affects tones on water surfaces.
2. Texture: Smooth texture for roofs of buildings. Grass looks smoother than a maize field or a forest. Mixed tones and textures suggest natural vegetation, derelict land, or periodic swamps.
3. Shadows: Give clues about the height of buildings or trees, depending on the time of day.
4. Shape: Features can be recognized from their shape (e.g., rectangular shapes are buildings).
5. Size: Big rectangles may be shops or factories, while small rectangles are usually houses.
6. Colour: On colour photographs, vegetation can be identified, with dry grass being light brown and trees usually dark green.
7. Pattern: Planted forests have a regular spatial arrangement.
8. Association: Similar or related land uses are often found together.

Unit 11: Orthophoto Maps

• Orthophoto maps are vertical aerial photographs modified to have:
  • A scale of 1:10 000.
  • Correct scale in all parts.
  • Ability to be joined together easily.
  • Added map items: contour lines, spot heights, place names, road numbers, power lines, and a co-ordinate grid.
• Newer orthophoto maps are in colour.

Unit 12: Orienting Maps and Photographs

12.1 Orienting a Map

• Orienting a map means positioning it so its north is actually pointing north.
• Use a compass or align landmarks on the map with their real-world locations.

12.2 Orienting a Photograph

• Orient a photo in the same way as a map in the field.
• Indoors, orient a photo with a map by comparing common features and transferring a direction line from the map to the photograph.
• Orienting the photograph is important because it is of greater value as a map supplement when its location and direction are known by the user.

Chapter 4: Geographical Information System (GIS)

Unit 13: Spatially Referenced Data; Spatial and Spectral Resolution

13.1 Spatially Referenced Data

• Data used in GIS must be linked to the location to which they refer, either by co-ordinates or by geographic features defined by their co-ordinates.
• GIS is considered a spatial database.

13.2 Spatial and Spectral Resolution

• Data used in GIS often comes in the form of images, showing data collected from both the visible and non-visible parts of the electromagnetic spectrum.
• Spatial resolution: The amount of detail a map or image shows.
• High spatial resolution means each cell or pixel in the image is small, resulting in a more detailed image.
• Spectral resolution: The range of wavelengths that an imaging system can detect.
• Invisible data can be made visible by using colours from the visible band.
• False colour Image allows us to look at details in areas of the electromagnetic spectrum which the human eye cannot see.

Unit 14: Different Types of Data

14.1 Point, Line, Area and Attribute

• Geographical features on Earth are one of three types:

1. Point features: Have no length or area.
   • Examples: A crossroad, a trigonometrical survey beacon and a spot height.
   • Location data: latitude (y) and longitude (x) co-ordinate pairs.
2. Line features: Have length but no area.
   • Examples: Boundaries, the middle line of a street, a pipeline, a power line and (on a world map) a river.
   • Location data: Points along it.
3. Area features: Two-dimensional shapes.
   • Examples: A farm, a park, a city block and a lake.
   • In GIS, the closed set of lines that defines an area is called a polygon.
   • Location data: defined by a connected sequence of x-y co-ordinate pairs, where the first and last co-ordinate pair are the same.

• Dimension: Measurement of length, width or height.
• Polygon: A many-sided figure.
• Attribute: Descriptive information about point, line and area features on a GIS map.

14.2 Raster and Vector Data

• GIS Image data is stored in two ways:
  • Vector method: Co-ordinate-based, using points, lines, and polygons.
  • Raster method: Cell-based, showing graphics as rows and columns of pixels.

14.3 The Advantages and Disadvantages of the Two File Formats

Vector Graphics

Advantages:

1. Images can be scaled up without losing quality.
2. Smaller file size.
3. Easier to handle.
4. Simpler to update.

Disadvantages:

1. Take a long time to create.
2. Don't show some shapes properly.

Raster Graphics

Advantages:

1. Great for showing very complicated images.
2. Come up on computer screens quickly.

Disadvantages:

1. Images become blocky when enlarged.
2. Need much more computer capacity.
3. Processing is slower.

Unit 15: Applications of GIS

• Climatology and meteorology use GIS as an essential tool.

15.1 Application to Climatology

• Climatologists use GIS to enter temperature and precipitation records from weather stations worldwide over long periods, showing an increase in surface temperatures.
• GIS uses past weather data to find climatic trends, projecting them to future dates through raster maps.

15.2 Application to Meteorology

• Weather satellites transmit images of weather conditions over Africa to ground stations, showing:
  • The visible view of the Earth.
  • The infra-red band.
  • Water vapour content of the atmosphere.
  • Rainfall rate.

15.3 Application to Oceanography

• GIS images show that the warm Agulhas current swirls into the South Atlantic Ocean, migrating across it and eventually adding to the Gulf Stream in the North Atlantic.

Chapter 5: Using Atlases

Unit 16: Using an Atlas Index

• All atlases have an index to all the names on the maps.
• The index tells you where to find a place in the atlas.
• Usually the order is name, page, followed by the position given as a grid square and/or as the co-ordinates (latitude and longitude) of the place.
• Grid square is a rectangle on the map identified by a letter of the alphabet for a latitude row, and a number for a longitude column, for example D7.

Unit 17: Locating Places on Different Maps and Comparing Information

17.1 Locating Places on Different Maps

• Atlases help us understand current issues and problems and make news reports more meaningful by showing where the news is happening and what it is like there.

17.2 Comparing Information from Different Atlas Maps

• Use atlas maps to illustrate answers to the following:

1. How is vegetation density or vegetation type related to total rainfall in Africa?
2. Why are people not spread evenly over any one continent?

Chapter 6: Fieldwork

Unit 18: Understanding Fieldwork

• Fieldwork observations and records give you first-hand experience of your local world, teaching you useful skills.
• Steps for fieldwork:

18.1 Observation

• Start with a question or hypothesis about a geographical issue.
• Hypothesis: A statement suggesting a relationship between variables to be tested.

18.2 Collecting and Recording Data

• Use primary sources (personal field investigation, unprocessed data) and secondary sources (processed data).
• Collect information by:
  • Gathering data by observation in the field, including measurements and counting.
  • Compiling and using your own original questionnaires for a social survey.
  • Using instruments like tape measures or weather instruments.
  • Recording the data in words, pictures, diagrams, maps, tables, or graphs.
  • Using data in books, census reports, newspaper articles, internet sites, questionnaires, and interviews.

18.3 Processing, Collating and Presenting Fieldwork

• Process your findings
• Distinguish between relevant (keep it) and irrelevant information (set it aside).
• Sort the relevant information into categories serving different parts of the issue
• Collate and analyse your findings
• What did you notice about … ?
• What did you find that differs from what you expected?
• Present your fieldwork findings
• What are the most important points you have learnt?
• How could these be organised into a report (written, oral or illustrated)?l
• What graphics would clarify your fieldwork report?
• What can be concluded from your study?