available, many of the project survey requirements would have been 
met by them or their enlargements* We have to bear this in mind in 
designing a production system for this series. We will revert to 
this aspect after discussion of some other factors affecting time 
required for prodcution. 
'TIME FACTOR IN PRODUCING A MAP: PRODUCT SPECIFICATIONS: 
MAP SUBSTITUTES 
It was mentioned earlier that one of our major concerns is to 
reduce the time taken to produce a map. 
It is common knowledge that the stage of drafting (fairdrawing) 
is costly as well as time consuming. It is here that map substitut 
es like qrthophotomaps and rectified photos come out with flying 
colours on two counts - reduced cost and reduced time. Misra (2) 
strongly advocates the use of photomapping for developing countries, 
the foremost reason is that this technique eliminates plotting and 
reduces drafting work as shown in Fig. 2. 
Aerial Photography 
FIG.2. PRODUCTION OF 1:50,000/1:25,000 MAPS 
CONCEPT OF STORED-CONTROLLED PHOTOGRAMMETRIC MODELS 
Referring to diagram below we see that first field season (Octo 
ber - April) and following recess (Office work) period (May - Sep 
tember) are spent in field control work, computations and aerial 
triangulation and the second field season in verification. Thus 
conventional methods will take a minimum of two field seasons to 
finish the job. This can be obviated by delinking the first field 
n