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reduce the number of flight lines, and consequently the necessary flying time, to less than
half the amount now needed in the scale 1 : 20.000 with the 18 x 18 cm film. Since the
available time is a critical point in this country, I believe it would be worthwhile also to
consider the problem from this point of view. There are a few disadvantages in this solution,
amongst which is, that the rectified diapositives would have a size 55 x 55 cm. With the
use of film, however, this would not be an important disadvantage.
As mentioned before, about 809, of the country is mapped by single photo-methods:
radial triangulation, rectification and drawing or scribing from and on rectified photo-
graphs. For the other 20%, which is the hilly part of the country, the Wild Autographs
A 6 and A 8 are in use. Contour lines are plotted directly in the plotting machine for this
area alone. In the flat area contours are interpolated between heights determined by
field levelling.
The ground control points for the base map are image points of sharp definition, iden-
tified in the field. The coordinates of these terrain points are determined by ordinary
surveying methods such as resection, intersection, traversing, etc.
The accuracy of these ground control points is about 30 cm, depending mainly on the
accuracy of the field identification of the point. No signalization of ground control points
is used. The vertical ground control points are levelled with an accuracy + 5 cm.
There exists a variation in the density of ground control points, depending on the type
TABLE 7. Distribution of time and cost over various parts of the map production
; ^ Prep. 'Total time and
Final map Cohtoürinterval Field- Work ?) Detail!) Drawing?) cost per km?
scale !) work ?) in Office plotting [or scribine|-- — -— -
m ee time | cost
1:12.500 or | 2!/, m or lev- | 48,3% | 7,095 3,9% 40,8%: 135,7 man | f155—
1 : 16.666 elled elevations 52,0% | 11,9% 2,8% 33,395 hours
l. Under "Final map scale" the final scale of the photogrammetric base map has been mentioned.
From this base map topographic maps 1 : 10.000, 1 : 25.000, 1 : 50.000, 1 : 100.000 are
derived. So the supplementary cost and time distribution for the drawing and printing of
these maps is not given here. Two scales are mentioned here because of the fact that the
Topographic Service is now in a transitional period from the scale 1 : 16.666 to 1 : 12.500.
2. The percentage under “Fieldwork” consists of the following components: field surveying for
ground control (horizontal and vertical), reconnaissance and spirit levelling for interpolating
contour lines and spot elevations.
3. This column consists of: preparation of fieldwork, radial triangulation, calculating of radial
triangulations, calculation of ground control points, rectifying and the assembly of photomaps.
4. To this column belongs only the stereoplotting with A 6 and A 8 of the very small hilly part
of the Netherlands. The monocular detail plotting from rectified photomaps has been placed
under "Drawing or Scribing".
9. These percentages consist partly of pencil and ink drawing on plastic sheet (astralon) from
rectified diapositives, partly of scribing on stabilene. The final control of the base map has
been incorporated here too.
General remarks regarding time and cost figures
The figures have been calculated from weighted averages. The upper row of percentages gives
an idea of the time consumption of the different parts of the mapping process, the lower row
indicates the distribution of costs. The large figures for fieldwork (48,3% time, 52,0%) are due
mainly to the fact that about 80% of the Netherlands is mapped with single photo methods
(rectifying), which doesn’t produce elevations. So nearly all spot elevations and elevations for
interpolation of contours must be obtained from field spirit levelling. In fact the two columns
"Detailplotting" and "Drawing or scribing" have to be added in our case because these two
steps coincide when the method of plotting of rectified images has been used.
27
