Features of maps
Contour lines
Heights on a map are represented by contour lines, continuous lines drawn on a map that join all the areas of equal height above sea level thereby indicating the shape of the landscape and gradient of slopes.
Other ways of indicating height are trig beacons, spot heights and colours. Using these for navigation will result in improved accuracy.
Trig beacons
These appear as a small triangle with a dot in the middle. They have a figure printed underneath or alongside which indicates the exact height above sea level.
Spot heights
Black dots usually on a hill, or on the highest point on a road, also indicate the exact height above sea level.
Contour lines and gradients
For the off road driver, an understanding of gradients and how they appear on a map is of great importance.
Where a series of contour lines run equidistant to each other the slope has an even unchanging gradient. Where contour lines are close together, the slope is steep and where contour lines spread far apart the slope is gentle. How gentle or how steep the slope is, determined by the vertical scale. If the contour lines are drawn at 100 meter intervals (this interval can be seen by reading the numbers written on each contour line) then with the aid of a ruler or a pair of dividers to measure the distance between each contour line, and by referring to the scale of the map, the angle of the slope can be calculated.
The distance between two points on a map is called the Horizontal Equivalent (HE). The difference in altitude between these two points is known as the Vertical Interval (VI).
To calculate the gradient of a slope, the formula is as follows:
• For example, the distance between two points (HE) is one kilometer or 1000 meters, and the height difference (VI) is 200 meters:
• Contour lines drawn at height intervals of 20 meters which are 2mm apart mean that the slope rises 20 meters every 100 meters. (2mm converted to scale of 1:50 000 is 100 meters).
• Likewise, contour lines drawn at height intervals of 20 meters
which are 50mm apart means that the slope rises 20 meters every 2500 meters. (50mm converted to scale of 1:50 000 is 2500 meters = 2 kilometers).
Another example is a one in one slope. This is a slope that for every one meter covered horizontally, there is also a one meter gain in height. The contour lines will be 0.4mm apart. For some off road vehicles, a one-in-one slope is technically possible, but the calculation of a vehicle’s ability to climb a gradient is measured when driving on a smooth concrete surface offering ideal traction to all four wheels. Driving over ground is very different, as there will be other obstacles to halt your progress.
Colours
Areas of height can also be coloured to assist in quick recognition of landmarks. Greater heights are normally shaded darker. You will notice that the edge of each shaded area runs along a contour line.
FINDING YOUR WAY WITHOUT A COMPASS
The Southern Cross
This constellation is best viewed between January and September because it is during these months that the Southern Cross is highest in the sky. So many people traveling from the northern hemisphere to the south often ask about this famous constellation that is represented in the national flags of Australia and New Zealand.
The stars of the Southern Cross constitute the constellation Crux, a Latin word meaning cross. It is the smallest of the 88 constellations in the sky. To face south, estimate the position on the horizon where the sun sets and then turn anti-clockwise for approximately 90˚. The stars of the Southern Cross are bright and well defined, so if you know what you are looking for it will be easy to locate. As shown in the diagram, the Cross is often seen lying on its side. There are also two bright stars, although not strictly part of the same constellation, that point to the ‘top’ of the crucifix, and aid in its location. They are called the Pointers. These two stars form the two front feet of the half-man, half-horse constellation of Centaurus. One of them, Alfa Centauri, is the closest star to our solar system and is a mere 4.3 light years from earth. (The measurement of distance when talking about the stars is the light year. It is the distance at which light travels in one year which is 9.4607 million, million kilometers).
The other star, Beta Centauri, is 330 light years from earth.
The Cross itself is made up of five stars with an area that appears
devoid of stars which is called the Coal Sack, which is what astronomers call a dark nebula. It is an area sufficiently opaque as to hide the
stars behind it.
Another interesting feature of the constellation is that the colour and brightness of each star varies, and this can be seen easily with the aid of binoculars. The stars are named after letters of the Greek alphabet, Alfa being the first letter. The others in order of brightness are; Beta, Gamma, Delta and Epsilon Crucis. The colour variation tells us how hot each of the stars are. Gamma Crucis is red, indicating a relatively cool star whose surface temperature is close to 2000˚C. Epsilon Crucis is orange and a little hotter while Alpha, Beta and Delta are blue white stars with surface temperatures exceeding 25 000˚C. As the diagram illustrates, by creating an imaginary line along the long axis of the Cross and a line perpendicular to a line drawn between the two pointers, the intersection lies directly due south (not magnetic south).
Finding your way
In the event that you are lost and you have neither map, compass or GPS, the most obvious thing to do is to follow your tracks and retrace your steps. But if you have been driving around lost for some time, following your tracks will probably be of little use.
The best course of action is as follows:
• Think back on landmarks that you drove close to before you became lost or disoriented. Rivers or dry river beds, small hills, villages or settlements, cattle or game watering holes and very tall trees are all things that you could make your way back to.
• Now calculate where north is. If you have no compass use the methods described previously. Finally, work out the approximate direction from which you have come and write it down; north-east, south-west etc.
Landmarks
Rivers and dry river beds.
The one thing that rivers, dry or flowing have in common is trees. Walk to the highest point that you can find and stand on your vehicle’s roof or climb a tree. Scan the horizon. A river valley will appear to be a long stretch of trees that are greener and taller than those surrounding them. Knowing where north is, write down the bearing of the trees to which you are heading. If the ground is flat you may have to re-establish north and/or look for the landmark periodically.
Villages and settlements
Paths with human footprints or litter will either lead to a settlement or a source of food or water. It may be necessary to walk in front guiding a vehicle along at walking pace.
Cattle or game paths
A little tracking knowledge or a book about animal tracks will help you determine whether a path is cattle or game. If the path is well trodden, it will probably lead to a watering hole or river. If it goes in the approximate direction from where you remember seeing a familiar landmark, such as a water hole, follow the path.
MAPS
Using a map designed for an application unsuited can lead to frustration.
Topographic maps
Normally 1:50 000 or 1:250 000, they are highly detailed with topographic features such as contours, rivers, roads and railways. They are used by anyone needing high detail and accuracy and are suitable for reading off the grid lines and inputting into a GPS. InfoMap Leisure-Traveler maps feature the accuracy of a topo map with road and tourist information with stunning digital 3D computer imagery.
Road maps
Scales range from 1:50 000 to over 1:1 500 000. Their primary task is to illustrate roads and tracks for the motorist. They are not suitable for accurate navigation using latitude and longitude grids.
GPS maps
Those published by InfoMap are often referred to as GPS maps. They can be regarded as a combination topo and road map. While the scales of over 1:500 000 does not permit the reading of grid lines and inputting into a GPS, they contain actual GPS co-ordinates. The coordinates are simply inputted into the GPS as way points. These maps are available in paper and electronic formats.
