direct projection type plotters in use. The large majority of these project the stereo model at 
five times the scale of the aerial negative. The anaglyphic projection equipment consists prin- 
cipally of the Bausch & Lomb Multiplex, the Balplex, the Kelsh plotter, and the Nistri Photo- 
mapper. The latter two instruments have been modified occasionally to be used at six and seven 
time enlargements as well as the customary five. Compilation of the stereo model with this 
type of equipment is usually directly at the scale of the projected stereo model, particularly for 
large scale mapping. Very little use is made of pantographs, coordinatographs, or other devices 
for changing the scale of the stereo model. 
The universal type optical train stereo plotters are much less common than the anaglyphic 
projection type. Their possession is restricted principally to the very large companies who can 
afford the necessary investment. Among these instruments in actual commercial use at this 
time can be found examples of production of Zeiss, Wild, Santoni and Nistri. It is interesting to 
note that in the greatest majority of instances where companies use this type equipment they 
are usually used in conjunction with the anaglyphic double projection type. 
Operational Procedures 
The primary purpose of this paper isto present the photogrammetric aspects of commercial 
practices. Therefore, discussion and description of such techniques and processes peculiar to 
the aerial photographic or ground survey procedures or even the cartographic drafting techniques 
now in common use will not be described except as incidental to the photogrammetric project 
itself. 
It should be understood in the following descriptions that the techniques described are those 
with which the author is most familiar and has observed personally. Without doubt techniques 
and procedures vary considerably among companies, particularly with respect to size. Never- 
theless, certain basic procedures are practiced in almost all U.S. commercial mapping organi- 
zations. In some instances they do not vary very much from the same procedures used in 
governmental organizations. In other instances variation is considerable. 
When a private mapping company has contracted for a particular mapping project it is cus- 
tomary for the client to have established a set of specifications. These specifications may or 
may not detail the type of photography and the equipment to be used. However, in almost every 
case specific accuracies are defined. In most cases at very large scales, such as 1:2400, 
1:1200 and 1:600, the accepted accuracy requirement calls for 90% of all well defined plani- 
metric positions to be within 1/40-inch of their true position and for 100% of all well defined 
planimetric points to be within 1/20-inch of their true position. For the vertical accuracy it is 
usually specified that 90% of all contours shall be within 1/2 contour interval of being correct 
and that no contour shall be in error by more than one contour interval. The use of a statistical 
value, such as mean error or root mean square error, is not customarily resorted to. The 
specification usually also states the completion date for the project. 
There is no uniform set of standard specifications in existence at this time which has 
official recognition and sanction. The closest thing to it is a publication put out by the United 
States Department of Commerce, Bureau of Public Roads, called a ‘‘Reference Guide Outline, 
Specifications for Aerial Surveys and Mapping by Photogrammetric Methods for Highways."’ 
This reference guide outline is endorsed by the American Society of Photogrammetry and the 
American Congress on Surveying and Mapping. It is so written that pertinent paragraphs can be 
extracted and used to set up a specificationfor a particular purpose. It has been extremely use- 
ful to a large number of public and commercial organizations in establishing accurately and 
clearly what their requirements are. 
After a company assumes responsibility for a project, the planning phase is initiated. This 
particular phase of the operation is very muchthe same whether the company be small, medium, 
or large size. Itfollows a more or less routine procedure if it is a conventional mapping project. 
The boundaries of the area to be mapped are established clearly and all existing ground survey 
control which has previously been located in the area is studied to determine its potential value. 
The flight altitude for the aerial photography is determined in a very routine manner dependent