Maps – Symbols, Scale, description, details Friday, May 27 2011

If we take an aerial view of some land, it is very difficult to work out any detail from it – slopes, heights, types of building, roads, telephone boxes and footpaths.  To further complicate things, when we need the map we’re rarely looking at it from above but from ground level.  We already know that the OS map has grid lines on it, but what else?

Firstly, the map is littered with symbols.  Ideally as a Scout you will get to know them all so that you won’t need to look at the key at the bottom (or at least, you can make a reasonable guess).  These symbols are all of some use – even knowing things such as County boundaries are useful (although not to the average walker – I’ve certainly followed the wrong one before now!).  Finding a Telephone box, or the edge of a marked footpath is excellent in being able to pin point where we are.

 

It’s worth knowing that when it is not possible to accurately position a symbol (e.g. a phone box) a line will be drawn to show where the item can be found.

A useful symbol on the OS map is the gradient symbols – the wiggly brown lines.  These show exactly what the ground is doing – so we can plan our route accordingly.   Below, I’ve created a Lego hill.  My walking Lego man can see (now he’s there) which way is easier to get to the top.  But without the map showing the grid lines he might not have known.  Like the Lego plates, the grid lines are drawn at intervals – slices of the hill.  I’ve drawn my “slices” and you can see how looking at this easily tells us which is the best route.

 

One of the other often missed gems on the map is the lines that show field boundaries.  Although these are simple straight black lines, they can help us in working out where we might be in the middle of a field with little to easily work out our position.

A Lego Hill from the side - you can see the slopes easily, how we would normally see it

The same hill from the top. It's much harder to work out from above

A contour diagram of the hill. As it would appear on an OS Map.

 

There is one last, important note.  Before you start using a map to plan your route, check its last updated date on the Key.  If you can’t see it, assume the map is out of date.  If it’s older than 5 years you should be prepared that there may be some changes – it might be that the public house has closed or that a new road has been created.

 

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Maps – Bearings Friday, May 20 2011

When we are on a walk, we will move from one point to another.  We do so on what is called a “bearing”.  This is often given as a degree of a circle – somewhere between 0 and 359 degrees.  Out on the walk, our bearings are calculated based on our compass; and here is our first important lesson.

Compasses (or at least the red needle) point to MAGNETIC North. Helpfully, there are three other types of North to confuse us – TRUE north (which is based on the spinning earth and we can use the sun and stars to work out) and GRID north (the direction that the blue grid lines on a map point to).  On OS maps, there is a note somewhere about the magnetic variation – this is because Magnetic north moves a little each year.  You may be interested to note that on sea charts the map-makers put notes on the maps to enable sailors to work out the magnetic variation quickly and easily.  Because this changes each year,  I’m going to mention it here, but not introduce any methods for working out the conversions; at the time of writing where I am this difference is quite small and would only complicate this introduction.

 

Working out the bearing on a map.

When we work out our route cards, we will mark a start point grid reference and the next point to aim towards.  If we draw a straight line between them (imaginary line, not a proper one!) we can lay the compass on this line, turn the red needle to follow the vertical grid lines (there are often straight lines in the compass circle to help get this accurate) and we can read the bearing direction.

Bearings - direction and North

use the compass to work out the bearing needed

 

Working out a bearing in the field – and using it

In the field, we might use a bearing in one of two ways.  If we’re following a route and we’ve got to a point that we know about, we can set the compass to the given bearing, look at where it’s heading and walk towards it.

Alternatively, if we are unsure of our location, we can use a bearing to make sure that we are walking towards something in a certain direction.

use a fixed point (like the flag) for a bearing - not the person on a bicycle!

Although we use the compass to set out bearings, we should not then use the compass to focus our attention.  If we do that, we will miss looking at the things we are walking past – or may miss something which may be important.  Instead, when we work out our bearing on our compass, we should fix our attention on a landmark close to (or better, in line) with that bearing point – and then walk towards that.  It is important (obviously) that the landmark is fixed – there is little point in walking towards a cloud or a sheep as they tend to move.

 

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Maps – Grid References Friday, May 13 2011

Being able to work out where you are is important in navigation – as you can then work out where you need to go next.  Maps are incredibly useful with stacks of detail (more on maps in a few weeks).  But knowing where you are is half the work – you also need a system so that you can tell others simply and easily.  There are many systems out there – Latitude and Longitude being a good alternative – but the one we will discuss here is the OSGB (Ordnance Survey GB) format.  This works with the system of Ordnance Survey maps in the UK.

For those reading this in other countries, you may be usingan alternate system which works subtly different, so this may be just of interest.

 

The UK is mapped in 100KM square blocks.  Each block has a two-character reference code.  This enables us to work out which area we are looking at.  Within each block, each “grid line” separating each kilometer is given a two-digit number, from 00 to 99.  In many cases for walking, the code letters are not used as it is rare that you would suddenly walk 100kms in a straight line!

We can use these two-digit codes to identify a single square kilometer.  This is known as a four digit grid reference.  The image below shows how we can work out the reference.  There are many methods for remembering which numbers to give first – I prefer to think of the letter “L” as it is written with the line going down first.  Just for ease of demonstration, I’ve used a chess board for the “map”.

4-figure grid reference

So using the image above, we can see the Lego Army man is at grid reference 0188.

Note that even the numbers 1 – 10 are actually presented as 01, 02 etc.  This is because we can easily work out what square we are discussing – if we said “188” we could mean 0188 or 1808… and they’re quite a way apart from each other!

 

But this accuracy isn’t that great – 1km is a big area.  We can be more precise by giving a 6-figure grid reference.  This is an accepted standard for walking; military uses may further go to 8-figure grid references.  GPS devices often present 10-figure grid references (but then report a 10m accuracy… so is no better than a 6-figure grid reference!)

To give a 6-figure grid reference, we first work out the four figure grid reference.  Then, we break down the square into 10 further blocks.  We can then work out (using the same “L” method) which one we are talking about.

6-figure grid reference

Although the Ice cream is obviously larger than a single square, I’ve marked in red the lines for the 6-figure reference.  Fortunately, this is the same square as we used for the Army man, so we know that the 4-figure reference is 0188. as the ice cream is 5 lines over (the 01 line is counted as zero) we start 015, then the ice cream is also 5 lines up – so the final reference is 015885.

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Reading 4 and 6 figure Grid References. Saturday, May 23 2009

As UK Scouts, we make use of the Ordnance Survey Maps as a standard for navigation.  So that we can get from one place to another, we use 6-figure “Grid References” to accurately identify the various points that we are talking about.  Using these references, we can create a route going from point to point (if you have a GPS device, these are often referred to as “waymarkers”).

 

On an Ordnance Survey map is a grid of Blue Lines going vertically and horizontally (there are squiggly blue lines as well, but they’re rivers and waterways )  Each of the blue lines usually has a number somewhere along its length.  The following is a map of Lees Wood Campsite:

 

 (Above: Lees wood map by Ordnance Survey.  See end of blog for further acknowledgements)

 Below is a simple grid diagram, with numbers along the top and the side.  In one square I have an eye – and I want to give you the grid reference for that.  Because it is such a big thing in the grid, I can give you a four figure grid reference  – 03 83.

There are many ways to help you remember the order of the numbers; the way I remember is drawing the letter “L” as you always go down first, then across.  Also, the zero in “03” is also important – if you miss giving it someone could read the reference as 38 3 – a wholly different place.

 

A quick exercise – what’s the 4-figure grid reference that has the two circles?

 

 

So that brings us onto the next challenge – when there’s only one thing in the square, four figures fine.  But that puts it into a 1km square area – not very accurate.  A 6-figure reference gives us a better accuracy – a 10m square area.

 6-figure reference isn’t much harder to do.  Let’s give a 6-figure grid for the Grey circle.  We know that the 4-figure grid is …. 02 82 (did you get that?).  What we do is divide that square up with ten more vertical and horizontal lines – effectively giving us a “decimal point”.  Just using a rough estimate, the grey circle can be calculated as :

02 grid line, plus it’s about 0.8 of the way across to the next grid line – 028

82 gridline, plus it’s about 0.3 of the way up to the next line – 823

 

So the 6-figure grid reference for the grey square is 028 823.

 

Soo… what’s the 6-figure grid reference for the square?

 

Other things to note:

1. If the object crosses the grid line, then the 6-figure grid reference will be a zero.
2. You may see a couple of letters in front of the grid reference – this defines a certain area and is especially important to start to pin point down the area that the grid reference refers to (in most hikes, this isn’t really needed as the map usually isn’t that big an area)
3. You can record 8-figure grid references; this is accurate to 1m square – and is mostly used by the military (and by GPS units… although many are never that accurate to start with!)

 

VERY IMPORTANT THANKS:

Lees Wood Map Reproduced from Ordnance Survey map data by permission of Ordnance Survey, © Crown copyright.

Image produced from the Ordnance Survey Get-a-map service. Image reproduced with kind permission of Ordnance Survey and Ordnance Survey of Northern Ireland.

 

 

Copies of Get-a-map mapping for teaching and classroom use:

Educational establishments may download sufficient copies of each map image as displayed on your browser to provide each pupil/student and teacher with an individual copy.

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Pioneering Challenge Saturday, Oct 11 2008

I had to change the main contents of this evening as we have the Pathfinder weekend coming up and wanted to give the Scouts some compass practice.

So the evening started with a game of “Poison Tree” – and it must have been a long time since we played it last as I had to explain ALL the rules, not just recap for new people.  That went well, although the scouts seemed to prefer going round the tree rather than dragging their colleagues through the pile of tyres…

We moved onto the main part of the evening.  We stuck Ordnance Symbols round the hall.  Each Patrol then decided (within the Patrol) which ten symbols they would use, then from their patrol corner worked out the bearing to the symbol.  For good measure they wrote down the bearing and the symbol.  All patrols moved clockwise round the hall.  The “new” patrol would then take a new sheet of paper (which only had the bearings on them) and worked out what symbol the bearing pointed to and what the symbol meant.  Unfortunately, because of the size of the hall, and because I don’t think the Scouts grasped the concept of bearings at the start, the bearings to the symbols weren’t particularly accurate.  However, the evening showed that the idea for the learning was reasonably sound, so we may come back to that again (with a few minor tweaks).

The Scouts then split up into those going on the Pathfinder weekend (who then started on their route cards) and those not – who were challenged to build a pioneering structure to get over an electrified line without touching it.  I was working with the latter group – and whilst they got what they needed to do - and I could see that the idea they were working on was sound – their team and planning skills still needed some work… but hey, that’s what Scouting’s about.

 

I also got back my first family history tree from Joshua – well done!  In telling me how the family had got together, it was clear that he had learned something more about his family than just who his grandparents were – which is excellent.

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