A map holder must be large enough to carry 9 X 9 in. (23 X 23 cm) aerial
photographs and should be made of masonite rather than metal (which is
uncomfortable to carry) or plastic (which may break when cold) (Fig. 2-2).
The same holder can be used for 8.5 X Il in. (21.6 X 27.9 cm) ruled paper
sheets for field notes (which are placed over the aerial photograph or map).
Field notes may also be taken in a separate field notebook, which can be
obtained in sizes small enough (about 4.5 X 7 in.) to fit in a large pocket. Or
may be preferable to take notes in a small loose-leaf notebook which is carried
in a leather case on one's belt. Engineers' field books and level bCX)ks are
available with high.rag or waterproof papers, which are essential for note-
taking in wet conditions. If separate sheets are used, as in the map holder
shown in Fig. '2-2, heavy ledger paper of top quality should be used in wet or
very dry climates (the latter eventually cause light, inexpensive papers to
disintegrate).