Adapted from a contribution made by Nuri Chorvat to the Confederation web site.
Send any comments to the maintainer Roger Caffin
This information is aimed at people who have not previously used maps for bushwalking.
1. Maps
Maps are generally produced by taking stereoscopic aerial photos of an area of land. These photos are then used to produce a topographic contour map which uses contour lines (lines of equal height) to show on a two dimensional piece of paper (the map) representations of height above sea level, together with natural features (such as mountains, rivers and vegetation) and man-made features (such as houses, high voltage transmission lines, bridges, roads and walking tracks). To make the maps easier to read, colour is used to distinguish different features. Eg. Green vegetation, red roads, blue rivers and creeks, yellow sandy beaches.
Every map will specify :
1. The year the aerial photos were taken,
2. The year that ground observations were taken to confirm features shown on the map
3. The year that the map was last printed
Each of these will usually be two to three years apart. Eg For Bundanoon - 1979, 1982, 1984.
Whilst most natural features (such as mountains and rivers) won't change, the man-made features can change. Eg. Farms gradually disappearing as new roads and housing developments replace them in growing municipalities, new fire trails.
Each 1:25,000 map covers an area of 15 minutes of longitude (across) by 7 minutes and 30 seconds of latitude (down).
2. Map Identification
Maps are identified using names and number systems. For example, the 1:25,000 map called "Bundanoon" (Second Edition) has an associated numbering system "8928-1-S". The combination uniquely identifies the map from all other maps in Australia, although "Bundanoon" would be sufficient for any bushwalkers within 100 kilometres. Maps are usually named after cities, towns or natural features. (Eg. Katoomba, Wollongong, Kangaroo Valley) The numbering system tells you the next larger map (scale of 1:100,000) "Moss Vale" 8928 which covers eight of the smaller maps in a series; 1-N, 1-S, 2-N, 2-S, 3-N, 3-S, 4-N, 4-S; with 1,2,3 and 4 rotating clockwise from the North position; and with N = North and S = South. Surrounding maps are also shown on the front.
3. Place Names
Place Names on the map (Eg. Mount Carrialoo or Bundanoon Creek) are generally approved and defined by the Geographical Names Act, 1966.
4. Contour Lines
These are lines which show points on the land which are exactly the same height above sea level. The shape of the contour lines represent the shape of the landscape. If contour lines are close together they indicate the landscape is steep. Contour lines which are far apart indicate the landscape is gently sloping. Contour lines can come together when vertical drops such as cliffs are shown. Every contour line which is a multiple of 100 metres is made thicker for ease of counting and somewhere along these lines at regular intervals will be printed the height (Eg 400). Contour lines can be used to determine which direction a river or creek is flowing. Elevations are shown to the nearest metre on the Australian Height Datum.
Bushwalkers will usually try and conserve their energy by minimising the amount of climbing or descending to be done during a bushwalk and sometimes will "contour" around a high feature such as a hill or a mountain. This means the walkers will try to walk around at the same height and not have to climb up and over the obstacle. However, the best views are generally seen from the tops of mountains.
5. Contour Intervals
The size of the contour interval determines the amount of information which could be useful to bushwalkers and the density of contour lines on a map. Contour intervals on 1:25,000 maps are 10 metres between contour lines and represent a good compromise between very little information (say with a contour interval of 100 metres) or too much information (say with a contour interval of 1 metre). Some maps use 20 metre contours which can be disconcerting if you are used to reading 10 metre contours. Small cliff lines may not be shown.
6. Scales
Bushwalkers generally use 1:25,000 topographical maps produced by the Land Information Centre (previously the Central Mapping Authority (CMA)) which is part of the NSW Department of Lands. These provide sufficient detail when traversing the land. Different scale maps are available such as 1:50,000, 1:100,000 and 1:250,000 but they cover too large an area and are really only suitable for use as road maps. Thus one square (4 cm x 4 cm) on a 1:25,000 map will represent a square on the ground of 1000 metres by 1000 metres. You will find a linear scale on each map.
7. Grid Lines
Grid lines are produced by the map makers to divide the map into 1000 metre by 1000 metre squares. The parallel vertical grid lines are aligned to be as close as possible with True North, although there may be some variation -typically up to 2 degrees east or west. The variation is given for the centre of the map. The vertical grid lines are defined to point to the Grid North, which is the top of the map. The parallel grid lines also make it easier to measure the angle of a bearing from one point to another when using a compass.
Grid lines have two digit numbers next to them around the edge of the map. These form part of a larger numbering system which can uniquely identify any point within Australia.
8. Grid References
The grid line numbers are used to give a Grid Reference (GR) which uniquely identifies a location (within a 100 metre square ) on a map. This degree of accuracy (nearest 100 metres along each axis) can be read easily and is usually sufficient for most bushwalkers.
The GR is formed by taking the two digit number of the nearest vertical grid line on the left of the selected point and estimating or measuring the decimal proportion to the next vertical grid line on the right. Then similarly for the horizontal grid lines and numbers starting from below the location. Remember to read the numbers Across first and then Down. This is an X-Y coordinate system which can use trigonometry to calculate angles and point-to-point distances.
For example, a location on the Bundanoon map with GR 693521 would mean that the nearest vertical grid line to the left of the location is 69 and then 3 tenths towards the next grid line on the right. Similarly, the nearest horizontal grid line below the location is 52 and then 1 tenth towards the next grid line above.
A Full Grid Reference (10 digits) would determine the location on this map to the nearest metre. Eg. 69312-52123 (These are not generally used)
A Universal Grid Reference (UGR) would add the Grid Zone to determine the location within Australia to the nearest metre. Eg. 56H-0269312-6152123
The numbers 02 and 61 can be found as small numbers in front of the normal 2 digit grid line numbers and form part of a 100 km by 100 km grid system which covers Australia. The numbers 312 and 123 are the respective distances (in metres) towards the next grid line. A GPS device could indicate your position in this format.
9. Grid Zone Designation
A Grid Zone Designation indicates that the map is located within a 6 degrees of longitude by 8 degrees of latitude grid. Thus "56H" (for the Bundanoon map) is the area between 150 to 156 degrees East (longitude zone = 56) and 32 to 40 degrees South (latitude zone = H).
10. Australian Geodetic Datum
The geodetic datum (or reference point) for Australian maps can be thought of as a point off the southern tip of Western Australia where the datum is defined to be X=0, Y=0 and Height=0. Thus all grid line numbers increase from west to east and from south to north on all maps. Note that Global Positioning Systems (GPSs) require the datum to be specified for the particular country (Eg Australia) that you are traversing in order to give a Universal Grid Reference for any location within the Australian Geodetic Coordinate System.
The datum point can change when the map makers want to realign the maps. For example, after a new series of more accurate aerial surveys are taken. For Australia the first survey was established in 1966 (hence the Australian Geodetic Datum 1966) but the datum was slightly moved in 1984 (hence the new Australian Geodetic Datum 1984). It is expected that the next series of maps will use the 1984 datum. The 1984 grid numbering system is presently shown as small grey numbers and tips of grid lines at the edges of each map. These are not presently used by bushwalkers.
11. Legend
This shows the coloured symbols on the map representing features to be found on the ground.
12. Key to Counties and Local Government Areas
Shows where the boundaries are for shires, counties and cities.
13. Rainfall Range
The chart showing the range of average rainfall for the area covered by the map can be used to determine what part of the year may be better for walking.
14. Temperature Range
The chart showing the range of average temperatures for the area covered by the map can be used to determine what part of the year may be better for walking, what additional clothing or water may be needed. This meteorological data is supplied by the Bureau of Meteorology.
15. North Pointers
These show the angular relationship between True North, Grid North and Magnetic North as shown diagrammatically or the centre of the map. Magnetic North will be shown correct for a specific year and the variation will be noted.
Eg. For the Bundanoon map, the following information is given.
16. Longitude and Latitude
Along the edges of each map are thick black and white lines. Each section of black line along the top or bottom represents one minute of longitude. Each section of black line along the left or right hand sides represents one minute of latitude. Longitude and latitude are given at the corners of the map. These are not normally used to specify position.
17. Map Reading Tips
1. It helps to align the map to face Grid North. This makes it easier to pick out features on the map and relate them to features in the landscape around you.
2. Water always runs downhill.
3. Maps tend to tear along the fold creases, so to make your maps last longer it helps to cover your maps with clear contact plastic (600mm wide rolls).
4. Remember to allow extra time for ascending and descending. As a general rule, 100 metres of climbing takes about the same energy as walking along level ground for 1 kilometre. Allow 15 minutes / 100m climbed (includes rest stops).
5. Fold your maps "concertina" style (Z folds) with the contours facing outwards. Two sections will fit inside a standard size map holder (or one section for the narrow map holders). Allows easy flipping of the map to adjacent folded sections (avoids refolding of the map and thus lasts longer).
18. Bushwalking Tips
It is generally easier to walk or find tracks:
1. Along the tops of ridges -because the ground is drier and hence less vegetation
2. Down spurs (ends of ridges) -less steep than down the side of a ridge
3. Along the sides of creeks and rivers - usually flat grassy areas
4. Along the bottom of cliff lines where sheltered caves and water pools may be found
19. General Tips
1. Keep your map and compass handy. Use a clear plastic map holder to hold both your map and compass. These are usually held around your neck on a strap or thin cord.
2. Protect your maps and compasses - when walking in the bush and at home.
3. Practise your navigation skills in a low risk environment. Leaders are usually happy to assist.