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).