Map Reading & Navigation

Map Reading Overview

• Author: B. Van Tonder

• Year: 2025

• Institution: University of Johannesburg

Purpose of the Study

• The purpose of this study material is to provide comprehensive knowledge about map reading including the construction, interpretation, and practical uses of various types of maps.

Background

• What is a Map?
    - A map is defined as a two-dimensional diagrammatic representation of reality.

• Construction of a Map
    - Involves the following steps:
      - Obtaining aerial photos
      - Conducting a field survey
      - Verifying information

• Types of Maps
    - Topographic Maps - Detailed representation of terrain
    - Geological Maps - Representation of geological features
    - Special Purpose / Thematic Maps - Includes route maps, political maps
    - Street Maps - Urban navigation-focused maps

Map Projections

• Types of Map Projections:
    - Cylindric
    - Pseudocylindric
    - Conic
    - Planar

Understanding Scale

• Definition of Scale:
    - Scale is defined as a unit-less ratio depicting how much larger or smaller an object or diagram is in relation to reality.

• Commonly Used Scales:
    - 1:10,000 - Ideal for search and rescue (not all areas are surveyed in this detail).
    - 1:25,000 and 1:50,000 - Most commonly used topographical scales, virtually all areas available.
    - 1:100,000 and 1:250,000 - Large scale maps suited for flight and shipping transports.

• Implication: Larger the scale, the more exaggerated map reading errors become.

Positioning on Maps

Longitude

• Definition:
    - Longitude refers to the position EAST / WEST of a location on Earth's surface.
    - Plotted using longitudinal lines.

Latitude

• Definition:
    - Latitude refers to the position North/South of a location.
    - Plotted using latitudinal lines.

Coordinate System

• Reporting Coordinates:
    - Reported in degrees, minutes, and seconds.
      - 1º (degree) = 60' (minutes)
      - 1' (minute) = 60" (seconds)

• Example of Coordinates:
    - E024°30’30.9“ (East-West coordinate)
    - S35°15’08.2“ (North-South coordinate)

• Reading Coordinates on a Map:
    - East-West coordinates are read from the top or bottom of a map.
    - North-South coordinates are read from the left or right margin of the map.

Practical Exercises

• Convert degrees, minutes, and seconds to:
    - Degrees minutes decimals
    - Degrees decimals

• Map Reading Practice:
    - Analyze given map data and coordinates.

Using Technology for Navigation

Combining Satellite Mapping with GPS

• Technology Integration:
    - Import KML map data into Google Earth for improved navigation.

• Significance:
    - Use new technology to aid navigation and search efforts.

Time and Distance Calculations

Calculating Real Distance

• Method:
    - Plug distances measured on a map into the scale to derive true distance.
      - Example: On a 1:50,000 map, for every 1 cm on the map, there are actually 50,000 cm in reality.
      - Result: 1 cm on a 1:50,000 map = 50,000 cm = 0.5 km.

Relationship Between Time, Speed, and Distance

• Relationship Defined by Formulae:
    - $ext{Speed} = rac{ ext{Distance covered}}{ ext{Time taken}}$
    - Example: A car moving at 50 km/h covers 50 km in one hour.

Direction and Bearing

Direction

• Definition:
    - Defined as named points of a compass: NW, NE, NNW, and so on.

Methods of Determining Direction

• Uses of:
    - Sun
    - Stars
    - Vegetation
    - Compass (utilizes Earth's magnetic field)

Understanding the Earth's Magnetic Field

• Core Composition:
    - The core of the earth is not solid; it consists of molten rock with high iron content.

• Magnetic Field Generation:
    - The flow of molten rock produces an electromagnetic field, which is affected by atmospheric conditions.

• Compass Functionality:
    - A magnetic compass aligns with the strongest magnetic field, typically the Earth's magnetic field (Magnetic North).

Bearing Explained

• Angular Deviation from Fixed Point:
    - Measured clockwise from 0° to 359°.
    - Bearing of 360° is equivalent to a bearing of 0°.

Magnetic vs True North

• Magnetic Declination:
    - Refers to the difference between Magnetic North and True North.
    - Current inclination indicates Magnetic Declination is west of True North.

Types of Bearings

• Magnetic Bearing (MB):
    - Measures clockwise using Magnetic North as the reference.

• True Bearing (TB):
    - Measures clockwise using True North as the reference.

• Forward Bearing:
    - Taken from one’s position towards a reference point.

• Back Bearing:
    - Taken from a reference point back to one's position (180° ± forward bearing).

Calculating Bearings

Bi-angulation vs Triangulation

• Bi-angulation:
    - System using two back bearings to calculate position.

• Triangulation:
    - System using three back bearings; preferred due to accuracy.

Reporting Bearings

• Preferences for two independent sources.

• Representation: Bearings can be True, Magnetic, Forward, or Back.

• Example:
    - 300°MFB = Magnetic Forward Bearing of 300 degrees.
    - 200°TBB = True Back Bearing of 200 degrees.

Practical Steps for Using Bearings

Plotting Forward Bearings

• Steps:
    - Shoot MFB correctly
    - Subtract magnetic declination to find TFB
    - Plot on the map correctly.

Calculating Back Bearings

• Steps:
    - Shoot MFB correctly
    - Subtract magnetic declination to find TFB
    - Calculate TBB: if TFB < 180°, add 180°; if TFB > 180°, subtract 180°.
    - Plot TBB on map correctly.

Rationalization

• Definition:
    - Understanding the reasoning behind navigation in map reading.
  

• Importance:
    - Essential for accurate and effective navigation.

Conclusion

• The material aims to provide an integrated approach to understanding maps, their projections, scales, coordinates, technological applications, and practical navigation strategies.