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.


Ideas to get you moving

I’ve been doing some work recently for a project Ordnance Survey is involved in called Ideas in Transit which is looking at how to unleash user innovation. Since doing more with less is something that most of us are going to have to get used to over the coming years, learning how to tap into and support these kinds of bottom up initiatives is going to be increasingly vital.

Thanks to peer reviews, wikis, blogs and price comparison sites, we can now dig up every last morsel of detail about a new product or service before handing over our hard earned cash. But what’s even more interesting is the fact that we can now get involved in product and service development in a way that was never possible before – think software, leisure, public services, citizen journalism and transport.

It’s this kind of approach to transport that the project is focusing on, with location information being a key element. The project is aiming to influence intelligent transport decisions at policy, social, personal and business levels, helping us all live better and more sustainable lives. We believe that there is a real chance for these often unique ideas to make a real difference to how we think and behave, helping to create a more sustainable future whilst at the same time freeing up public and private money from expensive, ‘top down’ initiatives. Sounds like a win/win situation to me!

Check out the Innovations Portal which showcases some of the best ideas from around the world. Among them is CycleStreets – a route planner designed by a couple of Cambridge based cyclists. It’s already a great resource that has been picked up by some local authorities, saving them tens of thousands of pounds compared to commercial alternatives as more people are using GI and maps.


Bath best for a city walk!


Bath Skyline – a row of Georgian houses

If you’re looking for somewhere great to go walking in your leisure time then you could head for the best route in Britain. Did you know that The Bath Skyline walking trail has been named Britain’s most popular city walk, in a new study by The National Trust?

Apparently, enthusiastic walkers questioned by the Trust suggested the 6-mile circular walking trail circumnavigating the historic city is the finest in Great Britain, closely followed by Clumber Park in Nottinghamshire, where green, open spaces lined with lime trees have become a walking hot spot.

Having recently spent some time in Bath I can definitely see what the fuss is about. The city is steeped in history and stunning views of Georgian sandstone buildings and rolling hills can be found on every corner, just what you need on a leisurely hike!

Jo Burgon, Head of Access and Recreation at The National Trust, says:

We’re finding that more people want to get out into the great outdoors but often need to be pointed in the right direction.

Bath Skyline and Clumber Park came out on top of a list of 130 walking trails in Great Britain, what better way to get some use out of your Ordnance Survey maps.


Could the future of maps be 3D?

Some incredibly clever people up in our Research team have spent part of a 3 year project working on this spectacular 3D map of the Bournemouth seafront. The work has been part of trials looking into how people might want to use 3 dimensional data for business, government and leisure in the future. I was gobsmacked when I first saw it.

The map was created using traditional GPS techniques combined with air and land based laser surveying, using something called Lidar, which works like light based sonar. Apparently this fly around is made up of about 700 million individual laser points!

If there was a 3D map of the whole country, can you imagine having a virtual tour of a town or mountain peak before heading off on holiday? Or, what about the emergency services being able to visualise the scene of an incident before they arrive? They would know about points of access, be able to see any obstructions and know the size and shape of any buildings involved. We’ve even spoken to someone who’s interested in renting roof space for solar panels. The possibilities are huge! How do you think you could use it?

There is still a lot of work to do before that could become a reality, such as how you would keep a 3D map up-to-date when we already make 5000 changes a day to the two dimensional mastermap of Britain, but its an exciting window into the future for using GI.

If you want to find out more about our 3D mapping project, you can read this article from the Daily Telegraph.


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.

Pathe news reel: how things used to be done!

A bit of fun and a fantastic window into the past here thanks to this Pathe news reel. I love the voice over and most of us can only dream of the motorway being so free of traffic! The technology, hairstyles and brown overcoats may have changed, as you can see from this film showing our modern techniques and taking us behind the scenes, but the passion, dedication and attention to detail are still here.

Just a note on accuracy though, I’m reliably informed that the film probably isn’t actually from 1953 since the first motorway in this country, the Preston by-pass, wasn’t opened until December 1958 and tellurometer didn’t come into use until 1957.