The making of a new generation of OS Explorer Maps

As the national mapping agency for Great Britain, Ordnance Survey is responsible for updating and maintaining the ultimate mapping data for the whole country. A combination of technological wizardry and human skill ensures that the challenges posed in measuring and recording changes in the fast-changing landscape are met – and the results made available to the public, businesses and government alike in the shortest possible time.

How fast is Britain changing?

It’s easy to imagine that the landscape changes relatively little – but that would be a mistake. While major new developments like the M6 Toll Motorway or high-profile buildings like the Scottish Parliament are obvious, every year more than a million changes to the British landscape need to be surveyed and mapped out by Ordnance Survey at the most detailed scale. New houses, road junctions, industrial buildings, tree plantations and the like have to be added, and at the same time some existing features have to be removed – for example, where buildings have been demolished or old quarries filled in. On average, no fewer than 5 000 changes are made every day to Ordnance Survey’s most detailed mapping database, with the results available to commercial customers very swiftly indeed – sometimes by the very next day.

How are the changes tracked and recorded?

Ordnance Survey has around 350 surveyors who are constantly out and about measuring and recording changes from a network of offices stretching from Inverness to Truro. They use high-tech equipment to gather information, including state-of-the-art theodolite ‘total stations’ with lasers to measure distances, and hand-held pen computers on which the latest changes can be plotted. They collect detail so fine that the shapes of individual buildings are clear – right down to the bay windows on houses. They also gather essential information like precise property addresses, new street names and leisure facilities such as new picnic sites. In urban areas they survey at the scale of 1:1250 – in Imperial measures, the equivalent of about 50 inches to the mile – and in most rural areas at the scale of 1:2500.

The surveyors also pinpoint locations at ground level by using Global Positioning System (GPS) receiving equipment to lock on to signals from a network of 24 orbiting satellites. This information is essential to ensure new features are properly mapped out in precise relationship to existing developments. Previously, a network of thousands of triangulation stations – including the familiar concrete pillars on high ground – was the bedrock for positioning calculations, but this method has now been superseded.

Information gathered by ground staff is complemented by an intensive programme of stereoscopic aerial photography, particularly of rural areas, which can be viewed in 3D. The resulting high-definition photographs (which show details as sharp as the pattern of white lines on roads) can then be overlaid with existing detailed map data to check where features have changed – for example, where a building has been extended – so that the most detailed mapping data can be updated.

Some information is also gathered from reliable and established external sources – for example, definitive public footpath and other rights of way detail are supplied by local highway authorities; and the extent of the new access land is defined by the Countryside Agency and Countryside Council for Wales. Also, many house-building companies share their development plans with Ordnance Survey so that the information can be held as a separate layer in the database to be verified and activated as soon as the developments are constructed.

What happens to all the information collected?

All the new information is sent to Ordnance Survey’s Southampton headquarters via landlines, where it is fed in to two computer databases. Each holds the data for a vast and incredibly detailed electronic map covering the whole of Britain, stretching from the Shetland Isles in the north to the Isles of Scilly in the south, replacing what were once 230 000 separate paper maps.

In one database the information held creates what is called Land-Line data; in the second, newer system it is formatted as OS MasterMap data. The latter is a revolutionary and extremely sophisticated database and online service in which the data is held as themed layers so that users can pick and mix the exact type and extent of the information they need. More than 440 million individual features of the landscape – like every house, pillar box and field – are held like individual pieces of an interlocking jigsaw, with each piece identified by a unique computer-friendly number called a TOID. This allows other people’s computer data to be linked to OS MasterMap quickly and easily for instant analysis – a vital tool for business and government alike. New layers of information are progressively being added to OS MasterMap, such as aerial photographic images which precisely match the mapping; data providing detailed addresses for more than 26 million properties, each geographically pinpointed in the map data; and integrated transport information covering many modes of transport.

How is the resulting data used?

Such highly-detailed information is used by a growing number of business and government customers who increasingly need an accurate, reliable geographic framework to help them provide effective and efficient services. Some examples of its use in the public sector range from the new web-based Transport Direct travel information service to the pinpointing of derelict sites suitable for house building; from identifying areas of deprivation to planning new access to the countryside; and from controlling the flow of urban traffic to helping the police detect crime pattern and catch offenders. In the private sector uses range from targeting marketing effort to calculating insurance risks; and from location-based services on mobile phones to in-car navigation and transport logistics systems.

Internally, Ordnance Survey also draws on its most detailed information to help it create and update smaller scale maps and data, such as the popular OS Explorer Map series.

So how are smaller-scale maps like OS Explorer Maps created?

Mapping at 1:25 000 scale (2½ inches on the map being equivalent to 1 mile on the ground or 4 cm to 1 km) has a long pedigree dating back to 1914. However, it was only ten years ago that the first experimental orange-covered Explorer map was published at this scale, and it is less than two years since the national collection of 403 Explorer maps covering every part of the country was completed. (Details of the unfolding history of this scale of mapping are provided later in this briefing).

Like the painting of the Forth Railway Bridge, revising maps is really a never-ending job. But as Explorer maps are primarily paper maps stocked by thousands of shops, it is sensible to gather sufficient new information on a particular sheet to justify its revision and the wholesale replacement of map stocks. There is, however, a regular cyclical programme for revising such maps, which tends to be about once every 4-5 years, meaning that in normal circumstances an average of two Explorer maps would be revised each week. Of course, if something really major happens in the interim that affects particular maps – like the building of the M6 Toll Motorway – the relevant sheets are revised more quickly.

The introduction of new countryside access land as a result of the Countryside and Rights of Way Act means Ordnance Survey is now in the process of revising 251 Explorer maps across England and Wales to show the areas where new opportunities to walk are being phased in. This is a huge and challenging task which needs to be completed in a relatively short period, with batches of information from the Countryside Agency and Countryside Council for Wales being supplied in stages to Ordnance Survey as the information for each region is confirmed by the relevant government Minister. In adding this intricate detail to maps, the opportunity is being taken by Ordnance Survey to merge the new information with existing access land owned by bodies such as the National Trust, Forestry Commission and Woodland Trust as well as some other landowners such as local authorities and national park authorities. Such access land is already shown on Explorer maps but in a different way. This new unity of appearance – a yellow tint surrounded by a narrow orange border – will illustrate the totality of access land and all the opportunities that are available to walkers.

Most Explorer maps cover an area of about 600 square kilometres, but some are double sided and cover larger areas. At Ordnance Survey, the computer data – the electronic artwork for each individual sheet of mapping – is currently stored in many separate layers. For example, there are individual data layers for public rights of way, tourist information, and hill contour lines.

Cartographers can overlay these layers at any stage of the process to ensure one type of information is not obscuring another – this is particularly important when deciding on the position of text such as place names. Having an eye for a good layout is an important skill for the specialist cartographers, as the end product must be pleasing to the eye as well as practical to the user.

Because they are integrating large amounts of fresh information from many sources – paper documents, computer data and maybe photographic evidence – cartographers have to be sure that every appropriate item of new information is incorporated. The usual technique is to work square by square through the map, incorporating changes to a single kilometre square before moving on. There are an average 600 such squares on a standard Explorer sheet, and sometimes on a full revision of a map, several detailed changes are required in each square.

Cartographers are helped in their task by the fact that any part of the map data can be greatly enlarged on the screen so they can work in fine detail electronically. Before the digital era, maps like this were created by hand using what was known as the ‘scribing’ technique. While computers have greatly speeded the process, and cartographers can use a digitising mouse to electronically track some of the detail on one set of paper maps to the data on screen, it is still very demanding work and needs an incredible eye for detail.

Cartographers also have to be selective in what they illustrate. While there are strict guidelines on what should and should not appear on particular scales of Ordnance Survey mapping to ensure nationwide consistency, on-the-spot judgement is frequently needed on how new information is shown and whether certain features need to be ‘generalised’ (simplified) so the map is not too cluttered. For example, the detailed shapes of individual new houses which appear at larger scales cannot possibly appear in that form on smaller-scale maps – for clarity they have to be merged into simplified blocks of property.

Sometimes cartographers need to amend the colours on the map to reflect a change in the way features are to be shown. For these latest Explorer map revisions, the way National Park boundaries are depicted at this scale is changing from a broad yellow band (which would clash with the new access areas and cause confusion for map users) to a narrower pale magenta series of dashes. This new style has been agreed with the National Parks.

There may also need to be changes to the map legend – the key. This time around, such changes include new information being added about access land and specifically where on the Internet users can go to seek up-to-date advice on temporary land closures.

Once the cartographers have made all the necessary changes, ‘plots’ (on-the-spot proofs) are produced and any necessary amendments are implemented for both clarity and accuracy.

The maps then move through a quality control process, so Ordnance Survey staff who have contributed information can be satisfied that all the relevant details have been incorporated. Each map is then checked="checked" by a dedicated quality controller to ensure overall quality and a consistency of approach between sheets in the same series.

Once quality checking is complete, the approved data is despatched in two directions: to be formatted as ‘seamless’ electronic data, and for printing as paper maps.

For the electronic data, the edges of the different sheets have to be matched up to create what is effectively a continuous map that can be used in electronic navigation aids, for Internet services, and for customised site-centred OS Select–Explorer walking maps that can be ordered via the Ordnance Survey website.

Data for the paper maps is imaged directly to printing plates to one of two large-format in-houses presses – a Nebiolo Colora 7000 and a KBA Rapida 130 five-colour press. The latter prints between 6,000 and 9,000 maps every hour. The paper used for the maps is specially selected="selected" for Ordnance Survey and is designed to withstand far more folding and unfolding than many more regular types of paper!

The flat maps off the presses are then folded on specially-built map folding machines and the protective card covers are subsequently attached, also using specially-designed equipment.

So that users will recognise which map sheets have been revised to show the new access information, the design of the cover is changing. Although the dominant orange colour that has become a feature of the Explorer series will be retained, it will be joined by a silver band matching the pattern used on the covers of other types of small-scale Ordnance Survey mapping. The new covers will also include the official access land symbol as well as a subtle change to the title of the series: as sheets are revised they will be known as OS Explorer Maps rather than simply Explorer maps.

Once the paper maps are complete they move just a few metres to the on-site Ordnance Survey distribution centre, where orders from wholesalers and major retailers are made up for despatch – with more than four million maps going through the doors every year. There are around 650 different paper maps in Ordnance Survey’s range, and bar-code scanners are used by staff to help speed the process of picking, packing and invoicing maps required by shops in Britain and overseas where the usual selling price is £7.49 a sheet – the equivalent of about 1p per square kilometre of detailed information.

Unfolding the history of 1:25 000-scale mapping in Britain

The origins of 1:25 000-scale Ordnance Survey mapping can be traced back to military maps of parts of Britain first produced in 1914, although these were not available for public use.

In 1938 it was proposed that a series of public maps at this scale should be produced “for selected="selected" parts of the country” to plug the gap between existing published Ordnance Survey maps at the one-inch and six-inch to the mile scales (1:25,000 scale equates to 2½ inches to one mile or 4cm to 1 km). It was suggested that such a series would be particularly useful in schools and, if the idea proved popular, the mapping might eventually extend to the whole of Britain.

The first experimental (or Provisional) maps at this scale appeared after the Second World War ended in 1945, and over subsequent years maps covering large parts of the country were published. It was, however, only within the last 20 years that full national coverage at 1:25,000 scale was achieved for the first time, including the remoter parts of the Scottish Highlands. Most of the original maps covered an area of just 10 km by 10 km, about a sixth of the area covered by most current Explorer maps, and they are remembered by map aficionados as the ones with the light blue covers.

Interestingly, because mapping at the 1:25,000 scale was not financially viable at the time, a Government committee suggested in 1970 that the concept of producing such maps for every part of the country should be abandoned, and that only sheets likely to be profitable should be produced. The outcry which greeted this controversial suggestion from groups such as the Ramblers’ Association led to a Parliamentary debate and the withdrawal of the proposal.

Consideration of ways of boosting interest in 1:25,000 scale mapping to cater for increasing leisure requirements led to the publication in 1972 of the first branded Outdoor Leisure map at 1:25,000 scale. This covered the Dark Peak area of the Peak District. Subsequently other Outdoor Leisure Maps were published, concentrating on national parks and areas of outstanding natural beauty.

To enhance the appeal of maps away from the national parks, many of the light blue maps were redesigned to cover twice the land area they previously covered and they were given green covers to distinguish them from their predecessors. They were also branded with the name Pathfinder – significant because, in England and Wales, the maps showed all rights of way, particularly country footpaths.

The first experimental Explorer maps were published in 1994, with five titles issued simultaneously covering parts of the Chilterns, Mendips and Northumberland. On average the new maps covered three times the area of their predecessor Pathfinders, and were six times bigger than the blue-covered originals at this scale. Users were being offered much more mapping for their money, and the additional tourist and leisure information added to the maps at the time made planning countryside walks and outdoor activity trips much easier. Over the following two and a half years, a further 26 Explorer titles were published for different parts of the country, several introducing or developing ideas to test the usefulness of the new-look maps to the public.

As a result of the huge success of these early, experimental Explorer titles, the decision was taken in 1997 to cover the whole country with Explorer maps by 2003, adopting a common set of features and design elements for consistency. The series was completed in the six year period and now 403 different maps at the same 1:25 000 scale – each with a distinctive orange-coloured cover – chart every part of the country from the Shetland Islands in the north of Scotland to the Isles of Scilly off the Cornish coast.

The detail of each map is such that every hamlet and village is mapped out as well as individual farms and other properties. Field walls and tree copses are highlighted, the routes followed by paths and tracks as well as every road and railway are marked out, tourist and leisure facilities are pinpointed, hill contours are tracked to show height and slope and now new access land designated under the Countryside and Rights of Way Act is being added to complement existing access land owned by organisations such as the National Trust and Forestry Commission.

To avoid ongoing confusion among map-buyers, the title Outdoor Leisure map was abandoned in 2002 and those maps were integrated into the Explorer series on the grounds that all the sheets were published to the same scale and carried similar information. This ensured an integrated series offering total national coverage.

Today, from around 650+ different paper maps published by Ordnance Survey, Explorer titles regularly occupy the majority of positions in the “Top Ten” sales charts with up to 3 million of them being sold every year.

Taken overall, the existing Explorer mapping series breaks even financially but many titles of less popular areas sell at a loss, despite the enormous popularity of the whole series among walkers and its value to country landowners and rural tenants. Ordnance Survey is committed to maintaining consistent national coverage at this scale so that wherever people go in Britain, they have the reassurance of an Explorer map – however remote the region.

Free Explorer maps for 11-year-olds

The Explorer series is also the one that is being offered to schools this autumn in what will be the fourth year of Ordnance Survey’s "Free Maps for 11-year-olds" initiative. It is anticipated that almost 780 000 children will benefit by receiving a personal copy of a relevant Explorer map for both home and school use. In the first three years of this programme, more than 2.3 million children have benefited in what is one of the biggest educational initiatives of its type in Britain. Teachers at each of more than 7 000 schools in the country where 11-year-olds are taught can claim the maps on behalf of their pupils by registering online at www.ordnancesurvey.co.uk/freemapsfor11yearolds

A design icon

At the turn of the millennium, The Design Council selected="selected" the Explorer series as one of its official Millennium Products, citing not only the high quality of the maps’ design, but also the way new technology has been harnessed by Ordnance Survey to produce them.

Map Index and online information

A free Ordnance Survey Map Index 2005 giving the titles and showing the extent of coverage of all 403 Explorer maps (along with all other small-scale Ordnance Survey maps) is available to the public on request by telephoning Ordnance Survey’s customer service centre on 08456 05 05 05 (local call rate) or email customerservices@ordnancesurvey.co.uk. A bilingual Welsh version is also available. There is also a free online search facility and map shop at www.ordnancesurvey.co.uk/leisure.