Tuesday 15 January 2013

The Mountainboarders Guide To Map Reading

[An unused article written late last year.  Shame for it to lie unused so is reproduced in full below (though a closing paragraph and disclaimer wouldn't go amiss)]




In this modern age, we are unlikely to discover anything truly new without going to the remotest jungles or the deepest oceans, but that doesn't mean that we can't all be pioneers in our own backyard.  Chances are in a land this large with so few mountainboarders means that there is a good odds you can find a local hill, wander up, ride down and become the first person to have ridden it on a mountainboard.  Then ride it again  clean to be the true Master of the Hill!

Perhaps you have conquered all of the local hills and are looking further afield for the next track to pick off, pioneer, then master, way before it later becomes a classic mountainboard location, ridden by riders from all over the country, all looking to replicate the success you have already gained.

But where to look in a country that is largely undulating but not necessarily mountainous; hilly but not necessarily accessible; accessible but not necessarily suitable?

A good starting point that should not be overlooked is local knowledge.  The UK loves to hike and everyone knows a good hill, or knows where the bikers like to go or where sledging is popular.  Where local knowledge is unavailable and where just going out and random wandering is not really a sensible option, then the next step is to pull out the OS map and get looking for clues.  Can you read a map?  Can you identify the terrain, footpaths, bridleways, roads, heights and likely gradients? Can you use the scale to estimate a rough distance and distinguish between a 50 metre dash and a 2km monster?  If not, read on!

Part 1: OS Maps - An Overview
Part 2: Estimating Distance
Part 3: Estimating Terrain
Part 4: Estimating Gradient

OS Maps - An Overview

Ordnance Survey (OS) provide UK maps at various scales, a popular one being 1:25,000.  Note that the smaller the second number, the greater the detail and in this case, a centimetre on the map represents 25,000cm (250m) in real life.  The exception to this are the symbols used to represent the various features; roads and rivers for example are a set width in order to be legible rather than being realistic.

Whilst other scales are available, for our purposes smaller scale maps provide insufficient detail and greater scale maps are harder, though not impossible to obtain.  1:25,000 map are available through bing.com and so are useful in this post for examples.

Usually, it is safe to assume that the top of the map points north (if you can read the writing then the map is probably the right way) and although there is a discrepancy between true north, grid north and magnetic north, as long as we are riding within the UK then we should be fine.  If you want to know more about some of the different poles and the differences between them, then the Ordnance Survey do a good job explaining:
http://www.ordnancesurvey.co.uk/oswebsite/support/knowledgebase/grid-north-magnetic-north-and-true-north.html

Please remember the following disclaimer though from Ordnance Survey:
"Whilst we have endeavoured to ensure that the information in this product is accurate, we cannot guarantee that it is free from errors and omissions, in particular in relation to information sourced from third parties."

In brief, use the maps as a guide but use some common sense!

Estimating Distance



OS maps show grid lines running both north-south and east-west marked in blue lines spaced apart in 1km intervals.  By mentally dividing these boxes by half or into tenths, smaller distances such as 100m or 500m can be estimated.  Remembering the principles laid out by Pythagoras, walking from the corner of one box to the opposite corner is therefore approximately 1.4km or 700 metres to walk diagonally across a quarter square.

Knowing distance is important for us.  It can tell us how far trail is from nearest parking, how long a trail may be, and crucially, how far it may be from the bottom of the trail back to the car again.

Estimating Terrain

Estimating what the ground may be like is far easier when you can use overhead photos to assist predictions, but a lot can still be read from using the map symbols.

PDF documents explaining all the symbols can be downloaded from the Ordnance Survey site at both 1:25,000 and 1:50,000 scale.
http://www.ordnancesurvey.co.uk/oswebsite/education-and-research/teaching-resources/map-symbols.html

An overview of the most useful symbols ones will be covered below.  Lets take my local hunting grounds, Allestree Park, as shown above.  Even if we were unaware of the area, some common sense and the fact that it is labelled a 'Park' and has a 'Big Wood' should give us some clues to the likely local terrain.  Lets now look at some of the symbols:

Parking.  Very useful if you want a starting point to store all your gear and want to do a quick reccee without lugging around all of your equipment with you.

Footpath.  In this case suggests that there is a 'Public Right of Way' across the site and so easy to get onto the land i.e. you don't need to fight through bushes to get to where you want to go.  Also useful if you want a well defined track which may be harder under foot and hence faster to ride.  Could also be a wet, sloppy mud-fest.  Keep an eye out for walkers when riding, obviously.

Other path types include:
Non-coniferous trees.  Here you can see from the overhead camera that a single tree icon designates several trees, or wood in this instance.  What is not clear from either the map, nor the overhead shot is how densely packed the trees are, or what the forest floor is like.  This is where going for a recce is the only way to be sure.  Coniferous trees are also shown on this map, though unless you ride into one of them, it shouldn't make a difference one way or another.

Other tree types include:

Golf Course.  Always popular with riders as the fairways are usually well maintained with the grass cut short.  Of course, how well you are welcomed will depend on the 'exclusivity' of the course, ranging from tolerated to actively hunted and removed from site.  Exercise caution.

Contour Lines.  This is a section in itself and will be dealt with in Part 4, Estimating Gradient.

Lake.  Don't fall in the lake.

Other possible symbols that might indicate a good place to ride include Mountainbike trail (the downhill parts anyway), Campsite (Good if you're in the middle of nowhere) or Viewpoint (suggests that it could look out over some lower terrain.

These are only some of the features shown.  If something looks unfamiliar, then check the symbol guide!

Estimating Gradient

Everything written above means nothing though if we get to a spot to find that it is flat as a pancake.  Fortunately, OS maps give a good indication through the use of contour lines.

These wiggly orange lines connect together areas of equal height and are indicated at either 5 or 10 metre vertical intervals.  If it helps, they can be thought of as being similar to isobars on the weather reports, connecting the areas of equal pressure.  Follow each line far enough and we should find a number equating to height above sea level.  By comparing the lines to those adjacent to it, we can determine where the high and low ground lies and the direction of the slopes.

From 'The SAS Survival Handbook', by John Wiseman are a couple of images that may assist the notion of representing terrain through the use of contour lines.

In a nutshell, where they are tightly packed together means that the terrain is steep, or even a cliff if the lines converge and where they are far apart, the gradient is slight.  We can even gauge if the shape of the hill is concave or convex by examining how the lines are grouped:

Lets take an example then using what we have learned so far.  Imagine that we have a 1km square and there are roughly 20 grid lines equidistant across the square with each one dropping by 5 metres each time.  From this we can determine that over that one kilometer, the height has dropped by 100 metres (20 x 5), equating to a 1 in 10 decent.  By this, we mean for every 10 metres ridden, you drop down one metre.  Not a bad decent; great if riding a firetrack, reasonable if riding short grass, may not be adequate if riding dense forest undergrowth.

It's worth mentioning that you cannot be over confident riding a trail 'blind' from map alone as the map will not show any terrain detail lower than the changes in contour lines.  For example, if the contour lines only show 10 metre changes in height, then a significant 5-metre drop could be encountered that would never have been shown on the map. Again, exercise caution.

No comments: