With peaks such as Catbells, Dufton Pike and Chrome Hill among them, The Fours, the list of England's 400-500m hills, is big on quality if not altitude. The list has recently undergone a major revision. Aled Williams and Myrddyn Phillips introduced it to UKH readers over a decade ago, and updates in the intervening years have now resulted in one of the most accurate hill lists available for walkers and baggers, they say. Here they explain the resources used to update this list, and the major changes they've made to it.

The 400m hills of England offer a grand variety of upland landscape, including mountain, moor, heath, grassland and high pasture. These hills take in the majority of upland areas the country has to offer, and visiting them will take you on a journey the length and breadth of England.

The listing of these hills has a long history going back to 2002 when the original compilation was uploaded to the RHB Yahoo Group file database. In more recent years the listing of the English 400m hills was published by Europeaklist and the Haroldstreet website. These latter listings were published in December 2013 along with an article on UKHillwalking:

It is now 22 years since this listing's original publication. Such a timeframe has given us opportunity to visit many of these hills. Not surprisingly when dealing with this height band, many of the recognised English upland areas have qualifying hills represented. These take in the farthest north-easterly part of the country with summits in The Cheviot group all the way to the south-westerly part with hills in Bodmin Moor. Between is a wealth of upland with the North York Moors, the Peak and Pennines, Yorkshire Dales, Lake District, the border lands with Wales and the wilds of Dartmoor all well represented.

This should be enough to keep any hill bagger happy for a year or more...

As well as enabling many of these hills to be visited, the 22 year timeframe has also given opportunity for the list to evolve. Its original compilation relied upon the latest 1:25,000 series of Ordnance Survey Explorer maps, with upland areas scrutinised for any qualifying hills. It took many hours of detailed concentration to finalise the original list. The days are long gone when paper maps were the sought after reference to create such a list. Nowadays there has been a revolution in accuracy which not surprisingly has been applied to most hill lists, including this one.

Revolution

This revolution takes in three main sources; independent surveyors, LIDAR and online mapping. The latter of these three is not as important as the other two, but it is still beneficial to cross reference numerical detail produced by independent surveyors and LIDAR analysis with online maps that now take in the Ordnance Survey series of Six-Inch maps, interactive mapping hosted on the WalkLakes website, Ordnance Survey mapping hosted on the Geograph website and the 5m contouring available on the DataMapWales.

There are now websites that host many photos of hills. Importantly these include summit photos that help in determining whether a large cairn has been modelled in LIDAR or whether the highest point of the hill is an artficial man-made construction such as a covered reservoir. All of this helps in producing a more robust list that 22 years ago could only be dreamed of. However, it is independent surveyors using GNSS receivers and analysis of LIDAR that has really revolutionised hill lists.

Attempting to determine the height of a hill for qualification to a list is nothing new, Munro was doing this over 100 years ago with a pocket-sized aneroid barometer. Nowadays independent surveyors using either a level and staff or more probably a GNSS receiver such as Leica or Trimble equipment are producing highly accurate drop, positional and height data.

However, it was not until the upland areas of England were fully covered by LIDAR (Light Detection and Ranging) that all hills in this list could be accurately assessed for height, position and importantly also qualification. The LIDAR technique relies upon measuring the distance between two points via a laser attached to an aeroplane. The time taken for the laser to bounce back is measured and enables the gathered data to be produced as a digital elevation model. The Environment Agency has been using this technique for many years determining areas at risk of flood and coastal erosion. As well as producing highly accurate numerical data that is now used in hill lists, the use of LIDAR has benefited other areas such as finding previously hidden rooms when mapping the interior of Egypt's pyramids and mapping the ancient Maya landscape, in the process finding hitherto unknown remains of early Mayan civilisation. It's handy technology in many fields!

The List

The above resources have enabled us to produce an accurate listing to these hills. This list takes in English hills 400m and above and below 500m in height that have 30m minimum drop. The main list is accompanied by a sub list entitled the Sub-Fours; the criteria for which are English hills 400m and above and below 500m in height with 15m and more and below 30m of drop.

There are 298 hills in the main list and 317 hills in the sub list.

It is not just the resources available that have evolved since this list's first compilation, as the list itself has evolved with all hills now listed in height to one decimal place and the criteria for the sub list now altered. Prior to this latest listing there were three accompanying sub categories, these included two categories of hills at and above 390m and below 400m in height and the Sub-Fours which took in hills with 20m and more and below 30m of drop. The two 390m categories have been dispensed with and the remaining sub category amended to take in hills with a minimum 15m of drop.

The result is a comprehensive list of the English 400m hills, with 615 included in all. That should be enough to keep any hill bagger happy for a year or more!

• The Fours – The 400m Hills of England is available to download from the Mapping Mountains website
• The list is also available as a Google Doc
• Also available as an online ticklist on the Haroldstreet website: The Fours and Sub-Fours