the high altitude models. These models are set in the universal first-order instrument and 
supplementary control is very carefully plotted in such manner that each of the four or more 
lower altitude models which cover the same general area as the high altitude model will be 
adequately controlled. This supplementary control can be established photogrammetrically with 
a surprisingly high degree of accuracy, both horizontally and vertically. The supplemental con- 
trol is identified on the lower altitude photographs and the X, Y, and Z coordinates are recorded 
digitally. They are not plotted. It is then only necessary to transform the stereo plotter co- 
ordinates to ground coordinates by a simple mathematical rotation and transformation computa- 
tion. These points are then plotted at the compilation scale in the same manner as field estab- 
lished points. Proper utilization of such technique can and has saved organizations considerable 
expenses in their field survey costs. 
Practically all stereo compilation in the commercial mapping field in the United States is 
accomplished with anaglyphic projection equipment. The majority of this equipment uses 5-time 
enlargement. Some of the smaller scale work is accomplished with the Multiplex at a total en- 
largement over the aerial negative of 2.4 times. There has also been some use of the Kelsh 
plotters and the Nistri Photomappers for compilation at enlargements of seven times the aerial 
negative. These very large enlargements are usually for what is referred to as strip maps 
where the entire area of the stereo model is not of interest but merely a band of terrain which 
usually runs through the center of the stereo model. 
The actual mechanics of stereo compilation is similar to all organizations, commercial or 
governmental, and requires no elaboration except, of course, that always the highest premium is 
put upon doing an acceptable task in the shortest possible time. The most valuable stereo oper- 
ator is not a man who can do the most accurate job but the one who can do acceptable work in 
the minimum amount of time. Normally theoperator will have his supervisor check his orienta- 
tion or the stereo model and when he has completed his delineation the supervisor will then 
again check the work. In some very small organizations, consisting of possibly only two stereo 
plotting instruments, the operators are practically independent of supervision and use their own 
judgment in determining the accuracy and acceptability of their work. 
The manuscript material upon which the stereo model is drawn and delineated is usually of 
specially treated low shrinkage paper. Recently very highly stable plastic materials have come 
into use which seem to be even more desirable from thé point of stability than the paper deriva- 
tives. When these materials were first introduced they were not readily accepted because their 
surfaces would not take pencil and ink marking satisfactorily. However, the available materials 
today are as satisfactory as the paper materials. With respect to the actual drawing that the 
stereo compiler does, it is customary for him to do precise but very rough drafting. The com- 
piler does not attempt in any way to dress up or refine the information which he draws. In this 
manner he spends as much time as possible actually doing the stereo plotting and a minimum 
amount of time in drafting. The rough but precise manuscript is then turned over to the drafts- 
man for dressing up and making of a finished drawing or map. 
By far the largest percentage of workturnedout by private mapping companies at very large 
Scales is a monochromatic map sheet on a transparent medium suitable for reproduction by an 
ammonia process. The task ofthe topographic draftsman is to trace from the manuscript onto 
the more permanent medium the information which has been extracted from the stereo model. 
The topographic draftsman performs the task of editing, refining, and symbolizing the material 
which the stereo compiler has put on the manuscript. Until recently and even at present much of 
the work submitted to the client has been on high quality drafting linen. Many of the clients 
specifically request such material but even now we see a definite trend toward using the new 
plastic materials as the base for the final map. These plastic materials have the advantage of 
being more stable and more permanent. The scribing techniques for topographic drafting which 
have evolved recently and have been used by so many governmental agencies is still somewhat 
a novelty for commercial private mapping organizations. It is not in common use at this time. 
Private photogrammetrists in the United States now face a stimulating challenge. A tre- 
mendous amount of work is yet to be accomplished. It is well known that the United States is not 
well mapped at very large scales. The government agencies are principally concerned with 
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