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| Trig Point Ben Vorlich |
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| Trig points show the height of the ground to the nearest metre above mean sea level |
| Triangulation Pillar (Trig Point) |
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Contours are imaginary lines on the map that join points of equal height above mean sea level. The height
between the contour lines is the vertical height and this will be always defined in the key of the map you are using.
Contour interpretation has two aspects: the spacing of the contours indicating the steepness and the curves they
make as they follow the hillside around indicating the shape of the land, known as relief.
There are two distinct elements in the representation of relief.
- Height.
- Shape
Besides contours, spot heights and trig points record their height in metres above sea level.
To summarise the rules for contours.
- Contours and spot heights, show heights in metres above sea level.
- The vertical interval on a 1:50,000 Landranger map is 10 metres.
- Every fifth contour (index line) is printed more thickly, to help with counting between contours and the
following of the lines around the feature.
- Where space permits, contour lines are numbered with their height, always printed so the top of the number points
uphill.
- On the 1:50,000 scale map, if the slope is to steep for the four intermediate lines to be drawn seperately,
some or all of them are missed out. The thicker lines are always present. When just one thin contour line is missing
the slope steepness is about 1 in 3.
| Numerical Representation of Height |
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NUMERICAL REPRESENTATION OF HEIGHT
Numerical height values for selected points are shown as follows:
Bench Mark. Bench marks appear only on large scale maps and plans as
a symbol with a height value stated to one or two places of decimals. The stated height is to the actual mark, not to ground
level. However the marks are rarely more than a metre above ground level.
Trigonometrical Stations (Trig Points). Trigonometrical stations usually
show the height of ground level to the nearest whole unit.
Spot Heights. Spot heights are located to
indicate ground height in ruling positions such as tops of hills, bottom of valleys, ridge points and saddles.
CONTOURS
On Ordnance Survey 1:25,000, Explorer Series, the contour vertical interval is found in the General
Information Section, under the sub-heading, Heights and Natural Features.
It is advisable to check this ,especially with this series of map sheet, as the vertical interval can differ.
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