Geoscience Reference
In-Depth Information
gradations matched to particular map scales, so no conversion
is needed and distances can be read straight off the scale. You
may need imperial as well as metric scales if mapping on old
base maps.
10.3 Location, location, location
10
Locating yourself accurately in the fi eld while mapping is of
paramount importance. Many of the basic skills involved have
been covered in Chapter 2, and these techniques are briefl y
expanded on here.
10.3.1 Equipment
Handheld GPS units are a valuable aid in mapping, but they
may fail in some situations (Section 2.6). If you are working in
remote areas, make sure you take spare batteries for the GPS (or
alternatively a solar charger for the batteries). It is worth
removing the batteries from a GPS unit that will not be used for
a while (i.e. weeks or more), as battery drain has been reported
for some units (you could keep a set of batteries bundled with
the GPS using a rubber band, lest you forget them). Always
take a compass (or compass-clinometer) as a back-up (Section
2.3.3, Figures 2.11 and 2.12, pp. 22-24), and consider taking an
altimeter, particularly if you are mapping heavily vegetated
slopes where bearings are diffi cult to take, or in an area with
few landmarks and/or poor base maps.
10.3.2 Using base maps
Good base maps may allow you to locate yourself relative to
features simply by inspection. Pacing out distances along a
linear map feature (i.e. road, stream, wall; see Figure 10.1) is
one way to locate yourself during mapping. You should
establish your average pace length, and pace steadily;
remember that stride lengths will be shorter on slopes than on
the fl at. In many cases, however, compass bearings can come
to the rescue (e.g. for triangulion as in Worked Example 10.2).
If you are already on a linear map feature (e.g. path, fence), you
can take a bearing on a landmark and fi nd your position from
the intersection of that bearing with the linear feature (Section
2.3.3). Choose a landmark on a bearing at a high angle to the
trend of the linear feature to improve accuracy, and remember
that landmarks closer to you (say, 100 m away) will result in
more precise bearings than distant features. Repeating the
process with a second landmark, if possible at about 90° to the
fi rst landmark, should verify your location. Remember that
compasses give the
magnetic
bearing to the feature, which
needs to be converted to grid north for comparison with the
base map (Section 2.3).
BEWARE! When using old
base maps, buildings and
roads may alter, and even
landscape features (e.g.
stream courses, woodland)
may be different to when
they were mapped.
