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ECONOMIC FACTORS IN INTEGRATED PHOTOGRAMMETRIC SYSTEM USA-5 
such instruments, which are used mostly for executing special assignments. But, 
for massive mapping operations, the ER-55 plotter is a practical and economical 
solution as a ‘“bread-and-butter” instrument. 
STEREOTEMPLETS 
In addition to the savings in control costs resulting from the use of the con- 
vergent ER-55 system, the introduction of the stereotemplet system (as op- 
posed to conventional slotted templets) for horizontal aerotriangulation achieves 
further economies by permitting greater flexibility in the placement of horizontal 
control points obtained in the field. Even if the number of points required re- 
mains the same, the increased freedom in positioning the points leads to econo- 
mies. The accuracy of pass-point positions obtained by this system has been 
found to be essentially equal to that obtained by instrumental stereotriangula- 
tion. 
SAVINGS IN STEREOCOMPILATION 
The increase in area covered by each convergent ER-55 model means that 
there are fewer models and less time spent in setting up and joining detail from 
model to model. The improved quality of the model permits an acceleration of 
the compilation process as there is greater certainty regarding the identification 
of detail and less need to refer to contact prints. The more favorable ray inter- 
sections in the convergent model leads to better repeatability of elevation read- 
ings and more accurate plotting of contours. 
The use of a variable-ratio pantograph greatly facilitates preparation of the 
original compilation at or near the publication scale for the map, even though 
the model may be several times larger, thus speeding up the compilation pro- 
cedure. 
SCRIBING TECHNIQUES 
In an important move towards economy in Geological Survey practice, the 
operation of drafting the original compilation of map detail on paper with pen 
and ink is being superseded by the technique of scribing the detail on a trans- 
parent plastic material coated with a special semi-opaque paint. The scribing 
technique consists of delineating the lines and symbols representing map detail 
with sharp tools that cut out the paint along the path of the scribing tool. This 
leaves a pattern of transparent map detail, the base remaining opaque except 
where it has been scribed. Copies of the scribed map are readily made by con- 
tact printing from this scribed base to a photographically sensitized surface. 
Scribing permits great flexibility of operations and lends itself to all sorts of 
conveniences and economies. Smooth, uniform copy is readily achieved with 
simple tools. Corrections are easily made by painting over the incorrect detail 
and scribing the correct detail. Edges are quickly transferred from one sheet to 
the other by contact printing. Notes can be made anywhere on the sheets with- 
out the need to remove them before copying. 
The original compilation can be compiled and scribed on two separate 
sheets, one for planimetry and one for contours. This permits convenient prepa- 
ration of two-color copies, printed on a scribing base, for use in field completion 
surveys. Necessary changes, scribed directly on the field copies, are readily 
transferred to the scribed originals. The largest single element of economy, 
however, arises from the fact that the original contour compilation sheet can, 
under favorable conditions, be preserved as reproduction copy.