- Permanent markers
- Oranges (or any fruit that’s easy to peel)
- Mobile phones or metal objects
Before you begin
- This is a great activity to run during an online session. Check out the advice on using Zoom and other popular digital platforms and the guidance on being safe online.
- Make sure you let everyone know what they’ll need in advance so they can join the session ready to go.
- Make sure everyone understands how to use a compass.
- Scout Adventures have some good resources around basic navigation and teaching compass navigation to others.
A tale of three norths
- The person leading the activity should welcome everyone to the meeting and mute them.
- Everyone should look at a compass. A compass uses a small magnetic needle, floating in a protective case. It points north as it lines up with the magnetic fields of the earth.
You could demonstrate on camera using one compass, or if people have their own at home you could talk through the information together.
- Everyone should look at a map and discuss what we mean by ‘north’. What is it and where is it? How is it shown on the map?
Everyone could use their own maps if they have them, you could email a copy in advance, or share your screen and use on online service like OS maps.
- The person leading the activity should explain that there are three different ‘norths’:
- True north is right at the top of the planet, at the geographic North Pole. The earth spins around this point so it never changes position. This north isn’t useful for navigating as we can’t find it with a compass.
- Magnetic north is the direction that a compass will point to. It’s slightly different from true north as the molten metals inside the Earth are constantly moving around, changing where magnetic north is.
- Grid north is the direction that the grid lines on a map point to. Magnetic north is used together with grid north for navigating.
Testing grid north
- Everyone should take an orange and a marker pen.
- Starting at the top of the orange, everyone should draw a straight line from the top of the orange to the bottom, as if drawing along the edge of an orange segment.
- Moving one centimetre to the right of the first line, draw another line from top to bottom.
- Continue working all the way around the orange, drawing straight lines from top to bottom until the orange is separated into roughly 10 segments.
- Draw a small ring near the top of the orange, crossing through all your straight lines.
- Move around half a centimetre further down from the top of the orange and draw another ring.
- Continue drawing rings until you reach the bottom of the orange. The whole orange should now be split into lots of different sized squares.
This is exactly how the blue grid lines on an Ordnance Survey map work. This splits the entire planet into thousands and thousands of small squares. Different areas of the planet are then given different labels, and each square within these areas are numbered. This gives each grid square on Earth its own unique identity.
- Peel the orange as carefully as possible, trying to keep it in one piece.
- Now try to lay the orange peel flat. The orange peel will have to tear and deform to be able to lay flat.
Maps have the same problem. Trying to show the surface of a sphere on a flat map doesn’t work without changing the surface. Map makers get around this by slightly changing the shape of the Earth when they print it, to fit a flat map. This leaves the problem that grid north on a map is different to magnetic north on a compass. Helpfully, map makers tell us the difference between these two norths on our maps.
- Everyone should look at a map to find where the adjustment for grid north and magnetic north are.
By adjusting our compass bearings by the amount of degrees shown on the map, we can convert from bearings on the map to bearing in real life, and vice versa.
- Everyone should look at a compass. What happens to the needle when it’s near a mobile phone or a metal object?
Anything metal will interfere with Earth’s magnetic field and make the compass point in a slightly wrong direction. This is called magnetic deviation.
- Everyone should think about an occasion where this could be a problem. It’s a real issue when using a compass inside an aircraft, which is full of metal and electronic instruments.
Depending on the plane and what else is in the cockpit, the magnetic deviation will affect a compass a different amount. Lots of smaller planes will have the magnetic deviation in degrees written next to the compass, to remind the pilots to adjust for it when taking bearings. Modern aircraft with digital compasses can adjust for magnetic variation automatically.
- Everyone should discuss how magnetic deviation applies to air navigation.
This activity was about developing skills. Knowing how to find a location using a map and compass is a great skill to have. It can help people find their way on an adventure and help them to be found if you ever need rescuing. Ask everyone to describe the three norths and say how or where they’d find each of them. Why are there three norths instead of just one?
This activity was also about solving problems, like how to make flat maps of a spherical planet. How did using the orange demonstrate the issue of transferring grid lines from a curved surface to a flat one? How do map makers get around these issues?
This activity can be stepped up by putting it into practice. Head outside and practise taking bearings on a map, adjusting them from grid north to magnetic north, and walking on them to see if you get to the right place. You can do this in reverse by taking a bearing from something in the distance, adjusting from magnetic north to grid north, and seeing if your compass now points to that object correctly on your map.
Another option for demonstrating the difference between grid north and magnetic north is to try and wrap a spherical object in a flat sheet of paper. This may work well for anyone with allergies or anyone that struggles with fine motor skills.
All Scout activities should be inclusive and accessible.