Author Topic: Explorers and Landrangers  (Read 17312 times)

Hugh Westacott

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Explorers and Landrangers
« on: December 12, 2013, 10:39:54 AM »
For many years I’ve studied and been fascinated by the various editions and series of Ordnance Survey maps in general use by walkers at scales of 1:63360, 1:50,000 and 1:25,000. In the course of correspondence with Paul Naylor of the Ordnance Survey, I discovered that of the 370 Explorer maps (they are numbered 101-470) plus the 34 OL Explorers that are not part of the sequential numbering system, which totals 403 sheets, 333 have contours at 5-metre intervals and only 70 have contours at 10-metre intervals.

I was astonished to learn this. It is well-known that there is more lowland countryside in Great Britain (England, Scotland & Wales) than there are upland areas, but I had not realized that there appears to be more than three times as much. But we have to be careful of the conclusions we draw from these statistics because the Ordnance Survey works on principles different from those of a geographer. For the Ordnance Survey, the choice of what contour interval to use is based solely on the need for clarity. If 5-metre contours were used on maps of mountainous areas, they would be packed so tightly together as to obscure other features and make map-reading difficult.

Bu this can give rise to some interesting anomalies. Many Explorers that employ a 10-metre contour interval, such as the four that cover the Lake District, also include quite large areas of lowland countryside outwith the mountainous areas. For example, the North Sheet of the double-sided OL4 The English Lakes: North-western Area  covers only a very small mountainous area in the south-east of the sheet with the remainder being a pattern of small fields, but the contour interval is 10 metres for the sake of clarity. I have some of the old Second Series 1:25,000 Pathfinder maps (which preceded the Explorer series) that cover this area of Cumbria. They were published in a smaller format measuring 20 x 10 km, compared to the 31 x 22 km of this particular Explorer, so many of them employ a 5-metre contour interval. This suggests that there may be an even higher proportion of lowland countryside in Great Britain than the Explorer map sheets with a 5-metre contour interval suggest.

Paul told me something else that surprised me. The 204 sheets in the 1:50,000 Landranger series have contour intervals at 10 metres, so of all the 607 Ordnance Survey maps in general use by walkers in Great Britain, 333 have contour intervals at five metres and 274 have contour intervals of ten metres. (Captain Paranoia will check my arithmetic!)

I’ve often wondered whether more people walk in lowland countryside rather than in the more demanding upland areas. My gut feeling is that lowland walking is the more popular pursuit but I have only circumstantial evidence to support this belief. Many people, like myself, walk in both types of countryside. And what is the definition of a walker? I meet people in the fields adjacent to my home who are exercising their dogs but they would probably not describe themselves as walkers. A possible clue might be found in the sales of maps but I doubt that, helpful as the Ordnance Survey staff is, they would be willing to reveal such commercially sensitive information. Also, many walkers, especially in lowland countryside, prefer footpath guides to maps. Others only walk with clubs.

Maps are an endless source of delight but I’ve wittered on long enough!

Hugh



captain paranoia

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Re: Explorers and Landrangers
« Reply #1 on: December 12, 2013, 12:53:25 PM »
One interesting aspect of this is when the maps move from paper to digital form.  With paper maps, the contour 'setting' is defined for the entire map.  With digital maps of areas covered by multiple map sheets, you see the transition from the 10m 'upland' contours to the 5m 'lowland' contours.  So you need to keep your wits about you to remember (or read) what the contour interval is.

I've also spotted some heights that are still in feet, that slipped through the metrication process...  Admittedly, these were on the 1:250k mapping.

Hugh Westacott

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Re: Explorers and Landrangers
« Reply #2 on: December 13, 2013, 07:03:02 AM »
The Captain makes an important point about the contour transition on mapping software. Fortunately, contours in lowland countryside are nothing like so important for navigation purposes as they are in upland areas where they may be the only significant feature. In lowland countryside the most important single feature is likely to be the field boundary. Before the introduction of 1:25,000 maps in 1957, the only suitable maps for walkers were the 1:63360 (the much-loved ‘one inch to the mile’ ) which were innocent of field boundaries and had a contour interval of 50 feet (15.24 metres). But somehow we managed!

<I've also spotted some heights that are still in feet, that slipped through the metrication process...  Admittedly, these were on the 1:250k mapping.>

A non-metric contour could not possibly appear on a Landranger. When the decision was taken to base all Ordnance Survey maps on the metric system it was decided that the scale of 1:50,000 would replace the 1:63360. In those days it took a long time to produce a completely new series so it was decided to speed up the process by making what was, in effect, a photographically enlarged version of the Seventh Series 1:63360 map. The main problem was the imperial contours so the decision was taken to keep the 50-feet contours but convert them to their metric equivalents rounded to the nearest metre. So the map had unhelpful contours such as 61, 76, 91, 107, 122, 152, 183 and 198 metres. Some contours such as 61 and 91 could only be printed on south-facing slopes otherwise they would read as 19 and 16!

Meanwhile, work was proceeding on the totally metric and completely redrawn 1:50,000 Second Series which was introduced in 1974. It was given the brand name Landranger in 1979.

I’ve not studied the 1:250,000 Ordnance Survey maps and only use them for car journeys. I’ve had a look at one which has a copyright date of 1993 which is long after the Ordnance Survey adopted metrication. Even so, heights, contours, relief tints and distances are all in imperial values. As they say in America ‘Go figure!’

Hugh

The proper pursuit of accuracy should not be confused with pedantry. Horace

Lost Soul

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Re: Explorers and Landrangers
« Reply #3 on: December 15, 2013, 01:59:00 PM »
Nothing is ever simply determined.

As noted above there are some anomalies in the way contours are displayed and the units of measurement that are used for heights.  One contour anomaly which is worth noting from a practical point of view for those who visit the Peak District area. 

OS 25K OL1 Peak District (North Section) Dark Peak has its contour intervals set at 10m.  Whilst OS 25K OL24 Peak District (South Section) White Peak has its contour intervals set at 5m.

Moving onto units of measurement.  OS still produces versions of their standard 250K maps with contours and spot heights in feet.  Contours at 200 feet along with hypsometric tinting in feet. These are for aviation use.  Where the international convention for specifying heights is to do so in feet.  Not only that the OS produced 500k aviation charts naturally use feet.

Turning now to France and IGN mapping.  For aviation charts they too use feet for defined heights as well as for hypsometric tinting.

And descending to the other end of IGN products.  Their 25K Carte de Randonnee uses 5m contour spacing as its base line (well certainly for those maps covering the Reims area) with selected bits of the countryside depicted with additional 2.5 m contour lines.  i.e in very flat areas.  Certainly helps with visualising from the map which way the gentle slopes are going and if the slope is continuous or makes a rapid change some place between two adjacent 5 m contours.

And what can we learn from this.  The obvious does not always prevail.  So Don't Assume! Check!  Check the legend on the map to accurately determine what the units of measurement are and what the contour spacing is before you set off.   

« Last Edit: December 15, 2013, 05:03:56 PM by Lost Soul »

Hugh Westacott

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Re: Explorers and Landrangers
« Reply #4 on: December 16, 2013, 06:46:25 PM »
Very interesting, Lost Soul!

I know virtually nothing about the Ordnance Survey 1:250,000 maps and so was fascinated to learn that height is expressed in feet for aviation purposes. Is this really so? Is it for the benefit of amateur pilots and hang gliders (or should that be 'hang gliderists'?) It reminds me that the the pilots of the early airliners on London to Paris route used to follow railway lines to get to their destination once they had crossed the Channel. There were several instances in foggy weather when a French farmer was surprised by a plane landing in one of is fields.

<OS 25K OL1 Peak District (North Section) Dark Peak has its contour intervals set at 10m.  Whilst OS 25K OL24 Peak District (South Section) White Peak has its contour intervals set at 5m.>

As I've pointed out, the great majority of Explorer maps have contour intervals at 5 metres. But the use of 5-metre contours on the Dark Peak map would pack them so tightly together as to make the map difficult to read.

Hugh

The proper pursuit of accuracy should not be confused with pedantry. Horace
« Last Edit: December 16, 2013, 06:48:38 PM by Hugh Westacott »

Lost Soul

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Re: Explorers and Landrangers
« Reply #5 on: December 17, 2013, 06:12:59 AM »
Hi Hugh, have been having a further look at OS 250K maps and have found out some further interesting things.  Am busy just now but will provide a considered post in a couple of days time.

LS.

Pete McK

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Re: Explorers and Landrangers
« Reply #6 on: December 20, 2013, 08:12:44 AM »
Look forward to seeing them Lost Soul having an Ordnance survey 1:250000 map which we bought some time ago in error thining it was 1:25000 - maybe we can now put it to use;)

Lyle Brotherton

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Re: Explorers and Landrangers
« Reply #7 on: December 20, 2013, 12:05:09 PM »
Contours are indeed fascinating and in my professional experience the most useful feature on maps in both lowland and highland areas.

In the military navigation which I instruct, they area mainstay as they are the permanent feature, it is amazing that even after the explosion of the most powerful ordnance in the world, land-burst thermonuclear devices, the topography of the adjacent land which changes significantly is confined and surprisingly limited.

The way in which Ordnance Survey defines and depicts them is an inexact science, which has evolved as surveying techniques have advanced and reproduction techniques have improved.

The changes metrification brought in converting Imperial units to SI in itself presented further challenges to their cartographers, as the original Imperial measurements inevitably included mathematical error corrections which were compounded if the figures were simply converted into SI units.

As always, all credit to this excellent agency for producing the finest National cartography in the world!

Forgive this lengthy treatise, which is only of interest to contour nerds such as me ;)

The current OS Standards for contour interpretation and depiction are:
   
Contours 1:25 000 (1 to 25,000) aka Explorer maps:

Contours are shown by orange lines and values in 50% monet magenta and 70% monet yellow.

The vertical interval (VI) of contours are either 5m or 10m.  At 5m VI, contours at 25m, 50m, 75m etc, are accentuated; at 10m VI, contours at 50m, 100m, 150m etc, are accentuated.

Updating of contours is only in the case of sheets falling in a subsidence area or where old quarries and pits have been re-landscaped and later information is available.

The number of contours can be reduced where they are likely to block in when they are printed.

Make up any unwanted breaks in contour lines.

Digitally produced contours are available from the Land-form Profile.

When both 5m and 10m contour vertical intervals occur within the component 1:25 000 maps of reformatted sheets, the most suitable interval for the sheet is selected. 

Holes In Contours
The following actions explain holes in the contours:

•   If it is clear that any part of the area within the hole is active, the description “Workings” is applied centrally in the hole on the Contour file (raster colour 7);
•   If the area can be positively identified as no longer active and the area has not been relandscaped, the description “Disused  Workings” is applied centrally in the hole on the Contour file (raster colour 7);
•   If the area has been relandscaped and disused workings are no longer evident the hole is left unannotated.  If contours are available they are re-instated.

Where detail on the source material, e.g. pit, quarry, corresponds to the hole in the contours the cartographer will ensure that contours do not encroach on the outer perimeter of the detail, pecks, cliff or slope symbol, which portray the feature.  Small portions of contours in close proximity to the hole are omitted in cases where they could be misleading to the map user.

Detail which is shown within a hole in the contours or within the area of an active working are not deleted unless specifically cancelled on the LS document.

If there is evidence of either partial re-landscaping or reversion to normal use, and the contouring date is the same as, or later than, the survey date of the source material, then such contours are re-instated if available.
   
Contours In Coastal Slopes, Cliffs, Cuttings, Embankments

Show these contours where running parallel with and through such features.  Contours crossing at an angle to the depicted slope or cliff are omitted.  Cases of doubt are referred to the QC.

Contours crossing small bank features, e.g. tumuli, are shown straight across such features where the height change is not significant.

Contours Crossing Quarries, Pits, Sand Dunes

Where contours are shown crossing quarries, pits or sand dunes they are omitted.

Contours Crossing Sand, Shingle, Saltings, Marsh

Where contours are shown crossing areas of sand, sand and shingle, saltings or marsh they are retained.

Contours Crossing Roads, Railways

Contours are not shown across motorways or dual carriageways.

Contours are shown crossing roads other than motorways and dual carriageways unless there is more than a contour interval difference between the road level and the adjoining ground level.

Contours are not shown across railways.

Contours In Relation To Water Features

Contours are not shown crossing double water features.

Contours not in sympathy with lakes, ponds or running water features are omitted or adjusted.

Contour Values

Contour values are shown; discretion may be exercised with regard to the positioning and density of values, but within the following rules:
•   Sufficient values are applied, without overcrowding the map, to enable the user to find the height of any contour quickly and easily;
•   Whenever possible values are applied in ladder formation continuing over hills and through valleys as necessary.  Such formations may be curved, slanting or straight;
•   The maximum distance between contour runs are 10cm.  In areas where the terrain is rugged and irregular, contour runs will tend to be closer than 10cm;
•   Values are positioned to read uphill; they are placed on straight parts of contours and clear of detail, names and vegetation;
•   Each value is placed astride the contour line which is broken to accommodate the value and leave a clearance on each side of 0.5mm.  In the case of small isolations the value is placed adjacent to the isolation in the horizontal position;
•   All contours cut by the sheet edge, all depressions and those isolations which need identification are numbered except where space is limited or the existence of a levelled surface height makes numbering unnecessary;
•   Adjust or omit values to clear grids, names and detail.  Rock ornament however may be cleared to accommodate values; and
•   Remove contour values where duplication occurs due to reformatting.

Contour Vertical Interval Note

Where the slope angle is less than degrees contours appears are at 5 metres.
      
   
Contours 1:50 000 (1 to 50,000) aka LandRanger maps:

Metric contours at 10 metre vertical interval are shown on all Landranger maps. They are shown in screened orange. See “Screens” etc specification. Contours are derived from the following sources:

   •   Contours surveyed at 1:10 000 scale and at 10m vertical interval.
   •   By interpolation from contours surveyed at 1:10 560 scale which are at 25ft vertical interval.
   (The following sheets in Northern Scotland still contain interpolated contours: 10, 11, 12, 15, 16, 17, 18, 19, 20, 22, 23, 24, 25, 26, 32, 33, 34, 35, 36, 39, 41 and 42).
   •   Field Revision.
   •   Development plans

Depressions, other than those indicated by zero height contours, are not shown.

In areas of close contouring the accentuated contours are given precedence, and some or all of the intermediate contours are omitted or broken depending on the space available.

The minimum distance between contours is not less than 0.4mm and the intermediate contours are normally omitted in the order lowest, highest, second lowest, second highest.

Depiction
Contours are shown as follows:

Those with a value of a multiple of 50 metres are line gauge 0.3mm

Other contours are line gauge 0.1mm

Zero height contours are line gauge 0.3mm

The minimum isolation size is 0.8mm.

The minimum clearance between contours and water is 0.2mm. Contours not in sympathy with lakes, ponds or running water features are omitted or adjusted.

Contours are shown in built-up areas.

Contours are not shown through areas of sand dunes and are broken where crossing motorways, cuttings and embankments, slope symbols, quarries, chalk pits, spoil heaps, refuse tips, dumps, landfill sites, opencast workings and double line water.

Contours are not shown through coastal slopes but are shown through coastal cliffs where running parallel with and through them. Contours crossing at an angle to the depicted cliff are omitted.

Contours are not broken for natural rock features.

Where contours are shown crossing areas of sand, sand and shingle, saltings or marsh they are retained.

Holes In Contours
The following actions explain adding new contours and holes in the contours:
   
When any spoil heap, opencast working etc becomes inactive, the original contours are not reinstated unless verified by Change Intelligence. Where workings are complete and the land has been restored and landscaped and new contouring is available, it is supplied through Change Intelligence using OS data, contractors’ plans or field survey. Digitally produced contours may be available from the Land-form Profile.

In areas of active opencast workings the description “Opencast Workings” is placed central to the area. In opencast workings which are no longer active but there are no new contours available, the description “Former Opencast Workings” is used.
   
Where detail on the source material, e.g. pit, quarry, corresponds to the hole in the contours the operator will ensure that contours do not encroach on the outer perimeter of the detail, cliff or slope symbol, which portray the feature. Small portions of contours in close proximity to the hole are omitted in cases where they could be misleading to the map user.

Contour Values

Contour values are on the same layer as the contours so if new values are added the contour will need to be broken.

All values are in metres.

Sufficient values are shown to enable the map user to find the height of any contour quickly and easily but without obscuring map detail or generating clutter.

The values are placed where easily visible and so that the map user does not have to trace a contour a long distance in order to find its value. The use of spot heights in finding contour heights is taken into account. Values are not necessary on small isolations containing spot heights.

In closely contoured areas, it is sufficient to number only the accentuated contours but in open and flat areas all contours are numbered. Contour values are shown in ULR 6pt on the Contours File.

The following points provide a guide:
* Values are always placed to read uphill.
* Values are not placed on sharply curving parts of contours, or where the depiction of the relief feature is affected adversely.
* The values are placed in "runs" or "ladders" where possible. The runs are curved, slanting or straight and not closer together than 7.5 cm nor further apart than 15 cm.
* The values in the runs are not placed closer together than 6mm, centre-to-centre.
* Where possible the position of values and runs are made easily readable from the south edge of the sheet. However this is not always possible and some have to be placed “upside down”.
* Each value is placed astride the contour line, which is broken to accommodate the value and leave a clearance on each side of 0.5mm. In the case of small isolations the value is placed adjacent to the isolation in the horizontal position.

Clashes with all black, blue and red detail, names and symbols, including rights of way should be avoided. Rock ornament however may be cleared to accommodate values.

Lastly, I love the fun the cartographers have had in sometimes creating imaginary contours and even writing their names in lines where separation would give little meaning. I will upload the examples I have been given by some of the cartographers at OS - Anonymously of course ;)
   

“Opinion is the medium between knowledge and ignorance” - Plato

Hugh Westacott

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Re: Explorers and Landrangers
« Reply #8 on: December 20, 2013, 04:09:16 PM »
Lyle, this is fascinating information! Is the source of your information in published form, or was it supplied to you privately by the Ordnance Survey?

<Contours are indeed fascinating and in my professional experience the most useful feature on maps in both lowland and highland areas.>

I’m genuinely puzzled by this statement. I cannot see the importance of contours for micronavigaion in flat countryside. What if there are no contours? A couple of years ago I walked sixteen miles in Essex coast from Burnham-on-Crouch to Bradwell and did not cross a single five-metre contour. There are considerable areas along the Essex, Suffolk and Norfolk coasts where there are virtually no contours for considerable distances inland.

I’ve been exploring the lowland regions of England on foot since 1949 which is before the introduction of 1:25,000 maps. It was difficult because field boundaries were not depicted and you could only follow a path if it were visible on the ground. The first 1:25,000 maps, which show field boundaries, started to be published in the 1950s and were a godsend because you could always establish which field you were crossing, and on which side of the hedge you should be.

I find that field boundaries are far and away the most important feature when micronavigating in lowland countryside. I’m only interested in contours insofar as they show the general shape of the land. I walk extensively in north Buckinghamshire which is intensely farmed and, for the most part, lacks significant hills (there is often several hundred metres between 5-metre contours). The only method of micronavigation that I know of is to walk from field boundary to field boundary. I’d really love to know of another technique.

Hugh

Lost Soul

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Re: Explorers and Landrangers
« Reply #9 on: December 20, 2013, 11:03:40 PM »
OS 250K Maps.   Having let the Genie out of the bottle on this one.
 
Up to the early 70s the OS 250K maps were known as the OS Quarter-Inch Maps, Scale 1:250,000 or about one inch to four miles (well that is what it says on the cover of the one I have before me).  The last iteration of them appears to have been the fifth series.  And 17 Sheets covered the whole of Britain. 

They are actually road maps for motorist.  Spot height and contours are in feet.  Hypsometric tinting with sun shadow shading adds relief and depth to high ground allowing visualisation of hills and valleys.  To me they are a lovely piece of cartographic art work.

In the 70s the 5th series was discontinued and replaced by the Routemaster Series of Britain at 1:250,000.  9 Sheets now covered the whole of Britain – double side printing being used.  Heights in feet, contours present but spacing not specified.  Hypsometric tinting with sun shadow shading retained but the colours are a bit more muted making the contours very difficult to see.  Maybe somewhere along the line the maps were metricated in terms of height information but I don’t know.

In terms of general offering on the shelves of Waterstones etc 250K maps are no longer available.  What are available to-day are OS Travel Map – Tour at 100k for most sheets and 175k for Snowdonia certainly.  Local Waterstones had a limited stock on display so can’t say for certain how widespread the use of 175k scale is.  These are motoring maps substantially de-cluttered of detailed topgraphical information.  Nevertheless hypsometric tinting with sun shadow shading is retained but using a different “style” to the old 250K maps such that Snowdonia certainly comes alive in a sort of pseudo 3D.  Heights etc are in meters.

Now the OS 250K map is not at all dead.  It is very much alive and well in two guises.  The first is that the 5th series, as described above, has lived on intact for several decades now as low level aeronautical charts.  And just in case anybody asks, they are up to date in terms of topography, roads etc.
 
The only difference between the aeronautical version and the old 5th series motoring version is that the former is overprinted with airspace and aerodrome information.  To use the airspace information you have to visual the sky in 3 dimensions in order to make sense of the airspace sectors.  Originally 18 handy manageable sheets covered Britain and Northern Ireland but some (12–ish) years ago that was reduced to 8 large unmanageable sheets covering the same area.

The other way that OS make the 250K maps available is in digital form.  I have via Memory Map a copy of the OS 250K Road Atlas 2012.  The maps have been de-cluttered to some extent.  Roads are now very prominently printed, hyposmetric tinting is muted, contour lines are quite visible.  Now here is the thing, the spot heights are in metres and the contour spacing is 61 meters.  i.e. 200ft.
 
What use are any of the above to the walking land navigator?  In my opinion not a lot of use on the hill, but they certainly allow for easy wide area visualisation of the terrain you might want to visit or even be in.  Far easier to visualise than trying to do so using 25K or 50K maps.
 
Hugh, you made the following comments: I know virtually nothing about the Ordnance Survey 1:250,000 maps and so was fascinated to learn that height is expressed in feet for aviation purposes. Is this really so? Is it for the benefit of amateur pilots and hang gliders (or should that be 'hang gliderists'?) It reminds me that the the pilots of the early airliners on London to Paris route used to follow railway lines to get to their destination once they had crossed the Channel. There were several instances in foggy weather when a French farmer was surprised by a plane landing in one of is fields.

Expressing height in feet is an international convention and all mapping agencies are required to use it on aeronautical charts.  And all vertical navigation is executed in feet.  Except Russia who insists on using metres.  All altimeters (except Russian) are calibrated in feet. 

So its not for the benefit of amateur pilots and hang gliders.  Its for the rigorous use off all who take to the air.  Your everyday BA 747 hauling itself across the Atlantic to New York is doing so by flying at heights specified in feet.  (Well flight levels actually, but they are just a short hand way of stating many thousands of feet.  FL245 is 24,500 feet).
 
Actually aviation uses a mix and match of units for linear measurements.  Heights are in feet including heights of cloud bases.  Runway lengths are in metres, visibility and horizontal separation is in metres – except in the US where they use feet for all 3, of course.  Navigational distances in Nautical miles.

Yes earlier aerial navigators most certainly followed the railways.  In those days there were no aeronautical charts so pilots took with them whatever maps they could lay their hands on.  Railways, even disused and torn up ones along with Roman roads, are a very prominent feature in the landscape and so are easy to pickout from the air and follow.  At night not so easy unless there is good moonlight. 

Anyway in the old days they were something of a standard navigation feature.  So much so that there was a proposal to whitewash the track beds so making them even more prominent; until it snowed of course.  That came to naught but the other navigational feature that was used was to paint the names of airfields in big letters on hanger roofs.  Or even arrows pointing the way to someplace.

Following a railway is in fact known as following a line feature – a line feature can also be a coast line, motorway etc.  There are strict rules for doing so.  You keep it on your left hand side, so you fly to the right of it.  Stops you bumping into other aeroplanes coming the other way.  We on foot of course call the general technique handrailing.

Back in the 1940s the Luftwaffe made good use of following line features to reach central London.  Entering British airspace in Kent they would pick up the east west rail line that runs dead straight for 40 miles from Ashford to Redhill.  There it would cross the North South London to Brighton Line.  Turn 020 deg follow that line for 15 miles and they were over the City of London. Nuf said.
« Last Edit: December 20, 2013, 11:06:40 PM by Lost Soul »

Lost Soul

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Re: Explorers and Landrangers
« Reply #10 on: December 20, 2013, 11:16:57 PM »
I find that field boundaries are far and away the most important feature when micronavigating in lowland countryside. I’m only interested in contours insofar as they show the general shape of the land. I walk extensively in north Buckinghamshire which is intensely farmed and, for the most part, lacks significant hills (there is often several hundred metres between 5-metre contours). The only method of micronavigation that I know of is to walk from field boundary to field boundary. I’d really love to know of another technique.

I fully agree with you Hugh.  I to do most of my navigation in similar territory.  OK not all landscape is as map.  Hedge rows (hence field boundaries) do get ripped up but if you know what to look for the tell tale signs of a former boundary are there to see.  Seemingly random trees in a field that when viewed from the correct angle are in a straight line.  Long low narrow mounds of earth where a hedge had once stood,  remnants of fence post.

Hugh Westacott

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Re: Explorers and Landrangers
« Reply #11 on: December 21, 2013, 09:12:04 AM »
Thank you, LS, for taking the trouble to provide such a helpful and detailed explanation of the uses to which the OS 250k maps can be put. I had absolutely no idea that they were used by present day pilots. I’ve learned a great deal from your post and I shall now see these maps in an entirely different light. This truly is a remarkable forum!

Hugh
The proper pursuit of accuracy should not be confused with pedantry. Horace.

Hugh Westacott

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Re: Explorers and Landrangers
« Reply #12 on: December 21, 2013, 09:14:55 AM »
One of the problems we run up against in this discussion is the use of terms ‘upland’ and ‘lowland’. ‘Upland’ generally refers to wild country beyond the limits of cultivation. ‘Lowland’ is more difficult to define. I’m using it to mean land that has been enclosed and improved for cultivation and pasture. We then run into a another difficulty. The term ‘enclosure’ also means, in England at any rate, the countryside that was converted from the mediaeval three and four field system by acts of parliament in the 18th and 19th centuries to give us the pattern of small fields that we now look upon as typical English lowland countryside. In fact, of course, land has often been enclosed for other reasons such as emparkment and the creation of property boundaries. Some of the field boundaries in the Lake District were created as a method of improving the land by removing rocks and ‘disposing’ of them by creating walls.

In many of the upland regions of England, including the Lake District, the Yorkshire Dales, and the North York Moors, there is enclosed countryside in the valleys and here I always micronavigate from field to field until I reach open country beyond the intake wall. In fact, with the exception of the Lake District, there is often a surprising number of walls that crisscross some of the highest and wildest countryside in England and I find that they are often more useful than contours for navigating.

Hugh
The proper pursuit of accuracy should not be confused with pedantry. Horace.

Hugh Westacott

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Re: Explorers and Landrangers
« Reply #13 on: December 22, 2013, 12:22:55 PM »
Lyle

The detailed information you have supplied about Ordnance Survey maps is very helpful and has taught me things about which I was ignorant. In particular, I was not aware that there was a convention that determined whether an Explorer used a 5-metre or 10-metre interval, and was under the impression that it was a decision made by the draughtsperson based on  clarity. You state <Where the slope angle is less than degrees contours appears are at 5 metres.> but have omitted the value of the slope angle. I'd dearly love to know this and also the bibliographic source of your information.

Thanks!

Hugh

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Re: Explorers and Landrangers
« Reply #14 on: December 24, 2013, 11:13:24 AM »
It would be so helpful to know the source(s) of the information supplied in Lyle’s post. It reads as though it was extracted from official Ordnance Survey material but, alas, some of the information is out of date.

Metric contours at 10 metre vertical interval are shown on all Landranger maps. They are shown in screened orange. See “Screens” etc specification. Contours are derived from the following sources:

   •   Contours surveyed at 1:10 000 scale and at 10m vertical interval.
   •   By interpolation from contours surveyed at 1:10 560 scale which are at 25ft vertical interval.
   (The following sheets in Northern Scotland still contain interpolated contours: 10, 11, 12, 15, 16, 17, 18, 19, 20, 22, 23, 24, 25, 26, 32, 33, 34, 35, 36, 39, 41 and 42).


All Landrangers are now sourced from 1:10,000 maps including the contour interval. When the first Landrangers were introduced in 1974, parts of Scotland were not yet surveyed for the fully metric !:10,000 series so an adjustment had to be made to interpolate metric contours onto the Landrangers from the imperial contours on the 1:10560 series. By 1994, the whole of Great Britain was covered by 1:10,000 sheets and it was no longer necessary to use interpolation on the Landrangers listed above.

I have a copy of Landranger 34 edition A3 with a copyright date of 1974 subsequently reprinted with minor revisions in 1993. On the map key appears the following statement that appeared on all Landranger maps of that period

Derivation of contours
1   From contours surveyed at 1:10,000 scale and 10m vertical interval
2   By interpolation from contours surveyed at 1:10560 scale and 25ft vertical interval


Yesterday, I checked all the current (B3) 2012 edition of the Landrangers listed above in my local map shop and without exception the derivation of contours was from 1:10,000 mapping alone.

Hugh