Basic Navigation Skills

The following series of eight introductory articles on navigation appeared in the Newsletter of the Melbourne Bushwalkers. There are questions relating to the articles for both expert and novice, with answers.

Possession of a map, preferably of scale 1:25,000 or 1:50,000, will be helpful.

Lesson 1 - Map Reading and Scale:

All maps have a scale, usually represented as 1:25,000, 1:100,000 or similar. 1:25,000 means that the map is 25,000 times smaller than the ground - that is, that 1 cm on this map is equivalent to 25,000 cm on the ground (or 250 metres) - so 4 cm is equivalent to 1000 metres (or 1 km) and vice versa.

Also almost all the maps we use have a grid which can be used together with the scale to judge distances and can give a feel for the size of things. Have a look at the map below, which has a 1km grid on it – that is the grid lines are 1km apart.

Novice Questions: (answer these questions by eye estimation, not by measuring)

1. What is the longest dimension of Rocky Valley Storage?
2. How far is it from Howman's Gap to Falls Creek?
3. Roughly how long (to the nearest ½ hour) would it take you to walk at 4 km/hr around the shore of Rocky Valley Storage?

► Show Answers  / Hide Answers:

 

 

 

1.  4 km
2.  about 4 km via the road
3.  about 3½ hours at 4 km/hr

(Notice that you were not told the scale of the map yet you were able to answer the questions using the grid – Conclusion: Grids are very useful for estimating distances on a map.)

Expert Questions:

You draw a line on a map from one point to another which is approximately to the north of you, where you want to go. You notice that the line is exactly parallel to the Magnetic North arrow on the declination diagram in the margin. Can you set the bearing without putting the ("Silva" style) compass on the map? What bearing would you set?

► Show Answers  / Hide Answers:

 

 

 

 

The obvious answer is that it is possible to set the compass to zero, or zero plus or minus the annual variation, however this is incorrect. On most maps the declination diagram it just that – a diagram which is not necessarily drawn to scale. For instance on the Dargo Plains – Cobungra 1:50,000 map the grid north-magnetic angle is quoted as 12 degrees, but it actually measures 20 degrees!

So the number of degrees quoted should be used, not the graphical diagram.

Next Lesson►