Geoscience Reference
In-Depth Information
10
(a)
(b)
Figure 10.4
(a) A home-made map case (
c
. 30 cm across) incorporating a rigid board for drafting, and a
hinged Perspex sheet to protect map sheets without obscuring them. (b) A second map case, which has a
clipboard base for A4-sized sheets. The hinge on the plastic cover is sprung so that it holds the position in the
photograph unless secured; the side panels help protect the sheets from the elements, while allowing access to
the fi eld map.
such as Mylar®, which allows multiple erasures without
degrading the sheet. Mylar® overlays for mapping should be
taped fi rmly to the base map (or aerial photograph) at the
top, but left untaped at the bottom so that the overlay can be
lifted to check features underneath. Always mark one or more
cross-hairs on the Mylar® sheet corresponding to a grid
intersection on the map, so that it can be replaced accurately if
disturbed. Mylar® should be placed shiny side down, so that
all working is done on the matte side.
Silva-type compass-clinometers can be used to measure and
directly plot azimuths on a map by setting the compass-
clinometer dial to the azimuth and then following the
instructions in step 3 of Figure 2.12 (p. 24) but a protractor is
also a useful addition. If you are using a Brunton-type
compass-clinometer a protractor is a necessary addition to your
kit. Structural data such as strike lines and lineation arrow
should generally be plotted accurately on the map in pencil in
the fi eld. At the end of the day they should be checked and
inked over. The numbered location of the data must also be
marked accurately, and linked via the locality number with
systematically recorded data in a notebook (e.g. Figures 4.10
and 4.11, pp. 71 and 73). If you are contact mapping (Section
10.5.2), the boundary should be drawn accurately in the fi eld.
Whether you use pens or pencils, map lines and data must be
sharp and clear. Mapping pens are more commonly used for
inking in at the end of the day's work. A ruler is useful to
measure distances on the map, but there are also 'scales' with
Some equipment is easily lost
when dropped, or left on the
ground by an exposure. Use
brightly coloured equipment,
bright labels, paint or sticky
tape to make your tools more
conspicuous.
