In the era of modern electronic convenience, we could be forgiven for thinking that we no longer need paper maps – or, for that matter, the ability to read them. While it’s one thing to blindly go towards a destination dictated to you by a little electronic voice from your dashboard GPS, it’s quite another to boldly go on a mission of exploration, discovering all that is around you.
Being able to read a map allows you to know exactly where you are and what surrounds you, it gives you the capacity to assist emergency services locating someone in difficulty, and it ensures you won’t get lost should your GPS’ batteries die.
Navigation is a skill that requires practice in the field, and can take years to master. Map reading is the first step in this endeavour. So let’s have a look at the basic principles.
WHAT MAP SHOULD I BUY?
The first step in map reading is choosing the right map for your journey. While most maps are general in the information they provide, to truly navigate you should be looking for a Topographical Map (typically A0 size).
These maps use up to eight colours to provide detailed, scaled and accurate graphic
representations of roads, buildings and urban development; railways and airports; names of places and geographic features; administrative boundaries and state borders; reserves, lakes, rivers, streams, swamps and coastal flats; or mountains, valleys, slopes and depressions and different types of vegetation.
Topographical maps reveal the lie of the land with contour lines, use a grid system based on latitude and longitude and are the result of someone having actually physically surveyed the area. So these are the most useful types of map you’ll find.
WHAT’S IN THE MARGINS?
Being able to read the map’s marginal information — and understand it — will help you comprehend the map itself. Among other things, these include:
The scale is found both in the upper left margin (after the series’ name) and in the centre of the lower margin. The scale gives the ratio of the distance represented on the map to the corresponding distance on the earth’s surface. For example, the scale 1:50,000 means that one unit of measurement on the map equals 50,000 units of the same measurement on the ground.
Contour Interval Note
The contour interval note is found in the centre of the lower margin. It’s normally below the bar scale. It states the vertical distance between adjacent contour lines of the map.
The legend is located in either the lower left or upper right margin. It illustrates and identifies the topographic symbols used to depict some of the more prominent features on the map. Topographic symbols are not always the same on every map, so you should always refer to the legend to avoid errors.
Grid Reference Box
The grid reference box is normally located in the centre of the lower margin. It contains instructions for composing a grid reference.
North Point Diagram
Topographic maps are printed so that ‘grid north’ (GN) points to the top of the sheet. This is indicated by the north point diagram which shows the angle between magnetic north (MN) — the direction the north end of a compass needle points corresponding to earth’s magnetic field — and true north, the direction towards the geographic North Pole.
The true north angle varies each year, depending on the position of the earth’s surface. It changes over time and varies with the age of your map. For map reading and navigation, the important angle is the grid-magnetic angle, the angle between GN and MN. This angle varies across Australia and you need to calculate it into your navigation planning.
When you take a bearing (choose a point) from your map, apply the grid-magnetic variation and set this ‘corrected bearing’ to your compass to accurately reach the destination and not some paddock a kilometre down the road.
WHAT ABOUT THE GRID?
Map readers use the grid to determine the bearing of a desired location.
Eastings are the vertical lines: the numbers written on each of the eastings increase from the left-hand side of the map to the right-hand side of the map (from west to east).
Northings are the horizontal lines and the number written on each of the northings increases from the bottom of the map to the top of the map (from south to north).
FEATURES AND CONTOURS
Each contour is a line of equal elevation. Therefore, contours on maps never cross. They show the general shape of the terrain.
To help the user determine elevations, index contours are in bold. Elevation values are printed in several places along these lines. The spacing between contours shows the finer detail of the land surface.
Contours that are very close together represent steep slopes, conversely, widely spaced contours or an absence of contours means that the ground slope is relatively level.
The elevation difference between adjacent contour lines, called the contour interval, is selected to best show the general shape of the terrain. A map of a relatively flat area may have a contour interval of 10m or less. Maps in mountainous areas may have contour intervals of 50m or more.
IDENTIFYING THE ‘SPOT HEIGHT’
On the top of hills, there’s a dot with a number written beside it. The dot will be inside a small enclosed contour line and the number indicates the height above sea level.
Trig points or triangulation pillars are also useful. The symbol for a trig point is a small triangle. They are actually real concrete pillars found in places such as the tops of hills or mountains.
So, there you have it: an introduction to map reading. If you spend time practising this skill and you learn to quickly and easily make the mental link between what you’re looking at on the ground and what you’re interpreting from the map, you’ll find that, eventually, you really know where you are...
Check out the full feature in issue #88 May 2015 of Camper Trailer Australia magazine.