Geoscience Reference
In-Depth Information
If possible use good quality base maps printed onto thin card
such as the 1:10,000 topographic maps available for the UK
(Figure 10.1a). These will be more robust for extensive use in the
fi eld, and will not suffer from distortion produced by copying.
Using one printed copy also ensures that all the data are in one
place, making it easier to assess the different lines of evidence.
Photocopies or photographs of fi eld maps can be taken at regular
intervals as insurance against loss, or a second hand drawn copy
maintained. If the base maps have lots of features or colour,
monochrome copies of base maps will show up geological data
recorded in colour more clearly, although some information on
the base maps may be harder to distinguish at a glance (e.g.
contour lines, fi eld boundaries). Figure 10.1 shows three
examples of topographic maps. Figure 10.1b, a 1:25,000
Ordnance Survey map, includes several features that could be
particularly useful for mapping (note that the 1 km eastings and
northings are labelled in blue on the map extract):
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topographic contours that defi ne landforms in the
landscape and give elevations;
point features on which to take bearings (e.g. cairn on
Meikle Crag at NX 342572, corner of coniferous plantation
at NX 348579, corner of wall on top of Pauples Hill at
NX 361583);
linear features to check compass declination angle (e.g. wall
running NE from minor road at NX 342580);
spot heights to calibrate altimeter (e.g. road junction at NX
357580);
location of specifi c exposures (e.g. on Craigdow Moor at NX
339572);
indications of vegetation (e.g. marshland at NX 351575;
scrub at NX 338575; rough grassland at NX 343574).
On this map extract bedrock is exposed mainly in the
southwest corner, with a few rock exposures indicated
elsewhere. However, other exposures such as those in streams
or roadcuts may not be shown. The exposure symbols do not
give a strong impression of the strike of strata in this case, but
on many maps exposures are elongate in the strike direction. In
the eastern half of this extract there are several distinct hills
with oval outlines (e.g. Spittal Hill at NX 357576), with their
long axes roughly aligned N-S. The lack of bedrock exposures
and their smooth outlines imply these may be features formed
from superfi cial deposits during the last glaciation, such as
drumlins. One way in which this hypothesis could be tested is
by examining the roadcut on the B733 at NX 362577, between
Gool Hill and Boat Hill.
BEWARE! When copying
base maps, avoid enlarging
them too much. No precision
is gained, because lines
simply become thicker.
