Grid References and Co-ordinates
Allows positions on the map to be described numerically. A complete reference gives map series number, sheet number, and a 6 digit grid reference. For example, a Grid Reference for Ward Island would be on the Lower Hutt NZTopo50 BQ32 567 269.
With reference to the diagram:
Using 6 digit grid references (dividing each grid square into 10 x 10 squares)
Drawn through points on the ground having the same height above sea level. The closer they are together the steeper the slope. The vertical distance between contour lines depends on the maps scale. On NZTopo50 series 1:50,000 maps it is 20 meters.
The direction towards the earth's geographic North Pole. Centre of rotation.
The direction of all vertical grid lines on a topographical map. Due to the distortion of transferring a spherical surface to a flat map there is an error between Grid North and True North. On New Zealand maps it is never more than 4°.
The direction where the North or Red end of a compass needle points. The North Magnetic Pole is in northern Canada and moving, and is roughly 24° East of True ans Grid North in New Zealand. This angle is different for all locations in the world. Refer to maps for local deviation angle and rate of change information.
Compass navigation (with SILVA type compass)
Orienting a map
- Rotate dial to line "N" or 0° with the Index Line of Base Plate.
- Place compass on map with North on dial aligned with North of map. i.e Vertical grid lines of map are parallel with orienting lines of compass, and orienting arrow points to north (top) of map. A common error when map is folded up, is to get North-South reversed - check text on map to make sure it isn't upside-down!
- Rotate map (must be level to allow needle to rotate freely) until red end of compass needle points at current magnetic deviation value (roughly 24° in New Zealand).
- Map is now orientated.
In Which Direction Do I Go?
- If you don't know where you are on the map, then perhaps you should try the next section first.
- Place compass on map with the bottom side edge of base plate on your current location.
- Rotate compass around this point until the top side edge (Direction of Travel, D.O.T. end) lies across your destination.
- Rotate dial only until orienting lines are parallel with North-South grid lines. (refer to step 2 of section A)
- Your grid (map) bearing can be read off the dial by the Index Line.
- With compass in hand and level turn compass (and body if necessary) until red and of needle points at current magnetic deviation (24°). Direction of Travel Arrow on compass base plate now points at your direction to travel.
Where Am I On The Map? (Lost maybe ?)
- You need to be able to see two identifiable features, preferably 90° apart for best accuracy. If you can see only one, then knowing what river you are next to or ridge top etc. may help pinpoint your location,
- Point D.O.T. (direction of travel) arrow of compass Base Plate at known feature (use edge for better accuracy).
- Maintaining Base Plate orientation, rotate dial of compass until red end of needle points at current magnetic deviation.
- Place D.O.T end of Base Plate edge on known feature on map.
- Rotate whole compass about this point until orienting lines are parallel with N0rth~South grid lines. (refer to step 2 of section A)
- Draw line on map from known point along edge of Base Plate.
- Repeat steps 2 to 6 for second known feature.
- Where the two lines cross is your current location.
- Repeating steps 2 t0 6 again, for a third known feature, increases accuracy further
How To Get It Wrong and Other Common Mistakes.
- Compass has been roughly treated, dropped, stored near magnetic materials (magnets, speakers, steel objects etc.)
- Compass not used level (needle not free to rotate).
- Compass used near metal objects (huts, pack frame eta).
- North end of compass dial points at South end of map when orienting. Le. upside down.
- Direction of Travel used in reverse.
- Start using maths or confusion with other methods people may have. A compass made for the Northern Hemisphere doesn't work too well down here. The needle is weighted at other end for level operation.
- Confusion between True North, Grid North and Magnetic North (i.e. variation in magnetic dip depending on where you are on Planet Earth).
- Lack of practice (probably the main reason).
Map and compass excercise #1 (use map NZTopo50 BQ31)
- What bay is in grid square 5022?
- What bay is in grid square 5324?
- What bay is in grid square 5322?
- What feature is at grid reference 382 218?
- What feature is at grid reference 412 277?
- What feature is at grid reference 363 293?
In Grid Square 3732, if you walked in a N.W. direction from Ohau Hill Spot Height 243m, would you be ascending or descending?
- Would you be crossing a steep slope or a gentle one?
- If you walked in a N.E. direction to Ohau R Light, would you be ascending or descending?
- In Grid Square 3929, the lowest point is in which corner? NW, N, NE, E, SE, S, SW, or W
- What height is it?
- Which way is the Waiariki stream running in Grid Square 3823 ?
- How far is it between Outlook Hill trig in 3725 and Mt Misery trig in 3927?
- How far is it between Mt Misery trig in 3927 and Terawhiti Hill trig in 3629 ?
- You are standing at Terawhiti Hill trig and wish to walk to the ore stamping mill at 375299. What Grid bearing would you be walking on?
- From Outlook Hill trig you want to walk to Mt Misery trig. What would the bearing be?
- From Mt Misery trig to Terawhiti Hill trig what would the bearing be?
- From Terawhiti Hill trig to spot height 329m in grid square 3630?
- Lyall Bay
- Worser Bay
- Breaker Bay
- Karori Rock light
- Golf course,
- Terawhiti Hill
- 3.5 km
Map and compass exercise #2 (use map NZTopo50 BQ31)
Try to answer these questions without looking at the answers first.
- What is at 490340?
- What is at 479348 on the same map?
- What bearing would I take to get from 1) to 2)?
- As above to go from 2) to 1)?
- How far is it from 1) to the centre of 2)?
- What is at 432220?
- From 2) what is the bearing to 6)?
- Where are you if you can see 6) at 180° and 1) at 46°?
- From where you live in Wellington what bearing is it to Oriental Bay fountain?
- Which direction is it physically? Use your compass. Is it what you expect?
- Orientate your map using your compass
- Can you identify any features you can see using the map?
- If you wanted to walk from Outlook Hill 378254 to Terawhiti Hill 363293, what route would you take to get there? Could you describe the route for someone else to use who doesn't have a map. ie Mention type of track, road, up, down, stream, ridge, directions, buildings etc.
- Where am I if I can see the peak at 363293 at 266° and spot height 201m at 422352 at 354°? Do you think I could really see these peaks from this point?
- Kaukau trig
- Te Kopehou
- Makara Hill
- Makara School (427301), Quartz Hill would block the view to 201m, while White Rock Hill would block the view to Terawhiti Hill.
Map and compass exercise # (use map NZTopo50 BQ31)
Try to answer these questions without looking at the answers first. You are at Mt Victoria trig (BQ31 504268).
- What can you seen in the direction of True/Grid north?
- What can you see in the direction of 341 degrees?
- What is the feature at 162 degrees at approx. 4km?
- What height are you at?
- What bearing is Point Jerningham (511279) from here?
- If you could see Johnston Hill (456294) at 300 degrees and the Trig A2LP (466259) at 258 degrees, where are you?
- Find the direction you would go to Wellington Hospital, as the crow flies.
- Using information from the map, describe the journey from Te Kopahou Trig (432220) to the building at 405253 if you were to walk it in a straight line. Describe features you would see, vegetation, terrain etc.
- Kaiwharawhara Point (504306)
- Stadium (496294)
- Airport terminal (515232)
- 196 meters above sea level
- 28 degrees
- Mt Victoria lookout
- 213 degrees.
- A rough description follows:- by no means all you could describe.