When developing a photogrammetric digitizing system, the following 
fundamental requirements must be considered: 
a) The system should offer a map product not inferior to existing 
graphical modes. 
b) The work in the analog plotter must not be more time-consuming, 
more tiring (physically or psychologically) for the operator, or 
subject to more blunders than usual graphical methods. 
c) The system must support several photogrammetric instruments and 
should incur no more than small overhead in implementation and 
running costs in order to make it economically feasible. 
d) The system should support on-line digitizing, graphic display 
and editing capabilities not inferior to graphic methods. 
e) It must retain the similarity and the ease of operation 
currently used in photogrammetric practice, so that the change 
over will be as transparent as possible. 
From the experience of the Topographical Survey Division, Surveys and 
Mapping Branch, Ottawa, Canada, the possible system configuration, 
hardware and software were described in detail in a previous publication 
(Allam, 1979,a). The basic system components are: analog photo 
grammetric instrument (or analytical plotter), digitizing devices, 
interactive graphic display and editing terminal, microprocessor, 
digital computer and storing devices. Software for data collection, 
transformation, interactive display and editing data storage, retrieval 
and manipulation are also essential. A schematic diagram of a 
photogrammetric digitizing work-station is shown in Figure 1. 
With regard to the method and extent of involvement of digitial 
computers and peripheral units for direct digitization from stereo 
plotting instruments, several feasible system configurations can be 
drawn up. In principle, they can be classified according to the number 
of stations (single or multiple), the capabilities for interactive 
display and editing, and the communication between the system components 
(uni-directional and bi-directional). The current trend in the develop 
ment of these systems is in the use of multiple stations with 
interactive display and editing terminals in a distributive computer 
network (Allam, 1979,b). 
COMPILATION FROM DIGITAL IMAGERY 
Digital compilation of topographic data from digital imagery requires a 
solution to the problems of digital image acquisition, and digital image 
processing for the derivation of topographic and planimetric detail 
(Allam, 1980, 1982). 
Digital imagery may be acquired by: 
a) on-line scanning of aerial diapositives using an automated 
photogrammetric instrument, 
b) image scanning using a microdensitometer, 
c) real-time data collection using airborne linear array cameras.