GI explained


We’ve extended our transport network dataset with urban paths

Great Britain’s roads are now busier than ever before and increasingly we’re all being encouraged to use our cars less often. That’s especially true here at Ordnance Survey where we’re being encouraged to car share or cycle once we move to our new head office.

And any visitor to London will immediately see evidence of the hundreds of thousands of pounds that have been invested in ‘Boris’ Bikes’ across the capital. The good news of course is that walking and cycling more not only helps reduce our carbon emissions but also improves your fitness and saves money on petrol.

So, to do our bit, we’ve extended our transport network dataset, OS MasterMap Integrated Transport Network (ITN) Layer, to feature paths for pedestrians and cyclists across every major population centre in the country.

A sample of our new Urban Paths theme

A sample of our new Urban Paths theme

That’s a total of 58,077 kilometres of walkways, the equivalent of seven times around the coastline of Britain!

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How to build an accurate 3D map

A few months ago I wrote about a 3D visualisation of the Bournemouth sea front that had been built by our Research department. It was all part of our work looking into the possible uses of three dimensional mapping and how we might try and keep a 3D mapping dataset current and up-to-date.

The team responsible for it have also been working on something else. This time it’s the London Docklands, built to be accurate to just a few centimetres across all three axis, X, Y and Z.

The Docklands

The Docklands

I spoke with the project’s architect, Jon Horgan, who explained the process behind it.

Firstly, we had to start with a solid foundation and the capture of features known as geomorphic vectors. These are used to create a very accurate terrain model, so that all the buildings and features will sit perfectly on the terrain, as they do in the real world.

The resultant terrain model was then used to add height to our OS MasterMap database prior to the photogrammetric capture of the 3D building models as well as features such as street furniture and vegetation.

Then real painstaking work of creating templates for some of the objects was undertaken where no stock 3D model existed. This included things like the lamp posts but also the cranes on the dockside and even the sculpture outside the Excel Centre entrance. The whole model is then automatically “textured” with our aerial photography.

Crucially, all of this work was done with only a block of stereo aerial photography and confidence in accuracies assured with GPS ground measurements.

It might not look like a modern computer game, but what’s important about this model is its accuracy. Just about every static feature is where it should be to within a few centimetres.

I particularly like the sculpture and you can also get an indication of the accuracy by looking at the shadows generated by the bill boards and fences.

The Excel Centre

The ExCel Centre

The big question remains of how exactly someone might use a 3D model like this. So, how would you use 3D?


Surveying the Glendoe Hydro Scheme

We recently caught up with two of our Inverness surveyors to find out what challenges they face in their remote corner of Scotland. They mentioned mapping the changes at a hydro scheme and I thought it might be an idea to find out how we updated our OS MasterMap database to show the Glendoe Hydro Scheme, Scotland’s largest recent civil engineering project. Craig and Dave faced a technical challenge in finding the best way to map the new and changed topographical features.


The Glendoe Hydro Scheme is located in the hills above Loch Ness near Fort Augustus and although a significant part of the project is underground, many new and changed features needed to be incorporated into our OS MasterMap database. These included the dam wall, the reservoir, all of the access and service roads, changes to water courses and their associated walls and sluices, and changes to the extents of vegetation and other surface features.


Glendoe as shown in OS OpenData

Glendoe as shown in OS OpenData


The area was originally surveyed using photogrammetry and then published at a scale of 1:10000. Peter Todd, Senior Production Manager at Ordnance Survey said, “Photogrammetry would be the normal approach to revising a large area of change in a remote location, but our surveyors chose to work on the ground for a number of reasons: the development was classified as a prestige site so we needed to update our data before the official opening with Queen Elizabeth II; with unpredictable weather in the area we couldn’t guarantee we could fly over and take the imagery in time; and the reservoir would not be filled with water until just before the opening, so we would need to survey the edge of the water by ground methods anyway.” Read More


Vernacular geography: What’s in a name?

There has been a bit of media coverage around in the last couple of week about some research we’re supporting at Cardiff University. It’s called Peoples’ Place Names, and they’re studying what’s known as Vernacular Geography.

What I might think of as the East End of London, or Shirley in Southampton, might be completely different from the next person, or at least different in ways I don’t realise. And that can still be the case even when a place has official boundaries.

For people that live or work in these places, the boundaries are often a matter of strong and passionate opinion. Have you ever met someone who, upon selling their house, was adamant that they didn’t live in a particular part of town?


Our sense of place can sometimes divide opinion. Image from Tim Green aka atoach via Flikr

And if you’re feeling really brave, why not start a debate about the exact location of The Black Country in the West Midlands? A lesson we learnt last year when we started printing the area on our OS Landranger Maps!

But in all seriousness, collecting these informal, vernacular place names could be really important in helping us build better place name gazetteers. These are not only important tools for us as map makers but also for the other organisations that rely on them, like the emergency services when responding to an incident.

When a 999 call comes in, knowing that King George’s Park is locally know as King’s Park or even “The Rec” could save vital minutes.

Last week in the Western Mail, Chris Jones, professor of geographical information systems at Cardiff University’s School of Computer Science and Informatics, said the data would also be very useful for online searching.

Last year we put The Black Country on the map, but steered clear of defining it's boundaries.

Last year we put The Black Country on the map, but steered clear of defining it’s boundaries.

He said: “Our language about space tends to be rather vague – lots of the way we refer to the world around us is vague.

“The idea of the site is to get people to tell us what names they associate with a particular place they live and give us postcodes and point to it on a map.”


Exploring our surveying antiques

The prospect of the upcoming move to our new head office has resulted in buzz of increased activity around the building in recent months. Just like when you move house, it’s been a good time to have a bit of a clear out and take stock of what’s been hiding under the proverbial bed or in the attic.

Well, part of that process has included cataloguing the many pieces of antique surveying equipment that have been accrued by Ordnance Survey over the past 200 years. Some of the items have played an historic role in the birth of modern map making in Britain and are irreplaceable.

To understand more about some of this fascinating equipment, I caught up with Ken Lacey, a surveyor by trade who now works in our education team. Ken was kind enough to give me a tour of what is rapidly turning into an Aladdin’s cave of cartographic memorabilia, with two pieces being of particular interest.

Here’s what Ken told me:

Ramsden 18” Theodolite

This beautiful piece of kit was made by Jesse Ramsden and bought by Ordnance Survey in 1795.

It is made to the same pattern as the two larger 36” theodolites, also made by Ramsden, and used for the construction of the Principal Triangulation, the very first national triangulation programme to cover the whole of Great Britain which began in 1791.

The 18" Ramsden Theodolite

The 18″ Ramsden Theodolite

The 18 inches refers to the diameter of the horizontal measuring circle. This circle is where you can read the angle between two points of interest. To read this angle you need to view graduated marks through 3 microscopes.

It was used in 1826 for obtaining the precise direction of the Lough Foyle base line, and from that time at Principle Triangulation stations throughout the British Isles.

This famously included on a platform over the top of the cross on St Paul’s Cathedral in 1849. When you consider that its dimensions are 540x720x550mm and it weights 28kg that is no mean feat!

Newlyn Tide Gauge

Ever wondered how we can give a height of an object above sea level? Think about it, the sea is rising and falling throughout the day, year by year and at certain times of the months and seasons we get a higher tide or a lower tidal point.

To calculate Mean Sea Level Ordnance Survey needed to record all instances over the full range of possible variations. That required at least one year of observations for a reasonable determination, but in practise it was calculated over a number of years. From these observations it was then possible to establish the point of mean sea level and from that then calculate the difference in height from this point to any other fixed location.

The Newlyn Tide Gauge

The Newlyn Tide Gauge

To take all the readings required to calculate Mean Sea Level, you needed a tide gauge. Examples were set up Felixstowe (1913), Newlyn in Cornwall (1915) and Dunbar (1917). Subsequently it was decided to solely rely on the tide gauge at Newlyn, which is the one we’ve got here in Southampton, stored out of use.

It was chosen over the others because it was situated in an area of stable granite rock and because the gauge was perched on the end of a stone pier at the harbour entrance it was exposed to the open Atlantic.

It was not therefore liable to be influenced by the silting up of the estuary or river tide delays, as was the case at the previous gauge at Liverpool.

It worked by recording the rise and fall of the sea with two floats attached by chains. The variations were recorded on paper attached to the rotating drum suspended from its centre.

One of the floats that was attached to the bottom of the gauge

One of the floats that was attached to the bottom of the gauge

Every height measurement in the country has been calculated based on the work of this machine.

Responsibility for the Newlyn Tide Gauge continued to rest with Ordnance Survey who provided a full time observer until 1983 when the station was handed over to the Institute of Oceanographic Sciences.

Why not check out some of our other stories from behind the scenes?


Time to rethink the design process: colour blindness and maps

There is a genetic disorder that affects up to 10% of men and about 0.5% of women. It impacts on their daily lives, often making the simple everyday tasks difficult and crushes the dreams of budding pilots and wannabe coast guards everywhere. Yes, it’s colour blindness. But for something that is experienced by a sizable minority of the population, colour blindness seems to play a relatively small role in the design process. Think weather forecasts, snooker and, yes, maps. The traditional rainbow of cartographic colours – greens for vegetation, reds for main roads and footpaths, and blue for motorways and rivers – can become indistinguishable, therefore making map reading really difficult.

It’s an issue that has been looked into by others, but up until recently it’s not something that we have been able to take into account when producing either our paper maps or our data. But all that has changed in recent times. With the launch of customisable data, like OS VectorMap Local, the user has far greater flexibility around how mapping is displayed and styled.

Colour blindness is the result of a deficiency of the specialised ‘cone’ cells in the eye that make colour vision possible. It is the most common genetic disorder among humans, with hundreds of thousands of people unable to tell the difference between reds and greens. Instead these colours appear as shades of grey or brown, making it difficulty to interpret colour-coded features. The Product and Cartographic Design teams here at Ordnance Survey have been working on colour schemes that can counteract this effect.

One of the styling exercises specifically for the colour blind, looks strange as it uses completely different colours for familiar map features. The result is a combination of purples, browns and oranges.

Simon Duquénoy, Technical Product Manager says:

“Cartography is a fine art, but the colours that have become so familiar to most of us are actually among the worst possible choices for those with colour blindness. Because of the technical developments in mapping data, we’ve been experimenting looking at how we can be more colour-blind friendly in our designs and colour choices.”

We are now developing a new colour palette for mapping that will work whether you are colour blind or not. This has been designed using software that can emulate the more extreme forms of the impairment. It has also been tested with a group of colour blind test pilots drawn from Ordnance Survey staff.While initially using the science of colour differentiation, we soon ran into familiarity issues – ‘Why is the motorway red ?’ asked the test group for example. Due to this we revised the colour style to make motorways blue again, but using a different shade to provide the contrast with other colours that is so important to the colour blind.

This is a major leap forward in cartographic design and leads us from thinking about specific accessibility for those with hidden impairments, to maps that are really usable by everyone.


What’s the difference between raster and vector mapping?

People ‘in the know’ when it comes to geography often talk about ‘raster’ and ‘vector’ mapping, but sometimes they forget that to ordinary people, these terms are pretty mysterious. So, I thought it would be useful, as part of our posts around GI explained, to try and describe the difference.

Raster mapping

OK, this is the easier of the two to explain. A raster map is basically a ‘dumb’ electronic map image made up of a set number of pixels. You can’t manipulate the information, move a place name around for example, and when you zoom into the map, it quickly becomes pixellated and unreadable, just like a photo taken on a digital camera. This extract from an OS Landranger Map is an example of raster mapping – full of detail and great if all you want to do is navigate or perhaps overlay some other information, like a walking route or flood plain.

This extract from a OS Landranger Map is an example of raster mapping

This extract from a OS Landranger Map is an example of raster mapping

Vector mapping

Right, now things get a little more complicated so bear with me. A vector map, like OS MasterMap, is basically a database of points, lines and polygons which collectively make up all the features on the map. It’s possible to assign each of these features extra information – perhaps demographic data and the age of the buildings for example. Using a Geographic Information System, or GIS, it’s then possible to do all kinds of analysis. For instance, you could ask the GIS to highlight only the buildings older than 50 years, with inhabitants aged between 30 and 40 living within 10 miles of a certain point. It’s the ability to do this kind of analysis that makes vector mapping such a powerful decision making tool.

I hope that makes sense. If you’ve got any questions, or can think of better explanations, please let me know!


What’s a grid reference?

Each week we’ll uncover some GI topics in GI explained. This week we’ll endeavour to explain grid references.

Every place on a map has a grid reference, so they’re pretty important when it comes to getting from A-B. Ordnance Survey developed the grid reference system and it’s used in all our mapping, from the raw data through to the paper maps that walkers, cyclists and even motorists love. Getting to grips with grid references is simple, just follow the points below, taken from one of our map reading leaflets.

  • A 1: 25 000 scale Ordnance Survey map is covered in a series of blue grid lines.
  • These grid lines help you to pinpoint an exact point an exact location anywhere on the map by giving a unique number known as a grid reference.
  • The vertical lines are known as eastings as they increase in value as you travel east on map.
  • The horizontal lines are called northings as they increase in value as you travel north on a map.
  • Four figuregrid referencesare a handy way of identifying any square on a map
  • Grid references are easy if you always remember that you have to go along the corridor before you go up the stairs
  • To find the number of a square first use the eastings to go along the corridor until you come to the bottom left-hand corner of the square you want. You then need to write this figure down
  • Then use the northing to go up the stairs until you find the same corner. Put this two figure number after the first one and you have your four figure grid reference.

This is an example of a piece of mapping showing grid lines. As you can see, it’s easy to pinpoint any location using a grid reference.

You might be interested in our map reading leaflets, which are great for kids and for the more advanced map reader alike.


Ever wondered about scale?

Map reading, including understanding scale, is taught at school in geography lessons, but for many of us this could be a bit of a distant memory and scale might not be a familiar concept. So, I’ve gone back to basics with our GI explained series to explain how scale relates to maps and map reading. Hopefully the points below will give you confidence to use a paper map even if geography lessons seem a long time ago…they certainly do for me!

  • The scale of a map shows you how much you would have to enlarge your map to get the actual size of the piece of land you are looking at.
  • For example, the popular OS Explorer map has a scale of 1: 25 000, which means that every 1cm on the map represents 25 000 of those same units if measurement on the ground (for example 25, 000 cm = 250 metres). See the extract below for an example of 1:25 000 mapping.
  • To make it easy, each OS Explorer map has 4cm to 1km written on the front.
  • Every 4 centimetres on a map is equal to 1km in real life. To make it even easier, the grid lines are exactly 4 cm apart so every square is 1km by 1km. 
  • Maps are made in different scales for different purposes. The 1: 25 000 scale map is very useful for walking but if you used it in the car you would quickly drive off the edge.
  • Maps at 1: 250 000 scale (note the extra zero) show lots more land but in far less detail.


If you want to know more about map reading or want to help your kids with their understanding of maps and geography, then you could download one of our map reading leaflets here.
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