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emulsion), a material adapted to engraving. A check of each sheet is carried out with
the aid of the coördinatograph, as well as the engraving of triangulation points, grid
ticks and the framework of the map sheet. For these Operations, a new coördinatograph,
especially adapted to the new processes, has been acquired. It is provided with saphires
for scribing, a light table and a vacuum frame to stick the sheet to the glass plate.
As this inscribed sheet is the base for all topographic map series, all topographic
features are engraved, with the photo's image as a guide, on true scale, i.e. without
exaggeration of roads etc.. So no dislocation of houses, ditches etc. takes place. Engraving
is done with a penholdertype scribing tool with stainless steel needle with a diameter
of 0.13 mm. Not before the topographer has checked the sheet with his field recon-
naissance and has approved of it, can the engraving be finished. The base map is now
ready. By a photographic enlargement to the scale 1 10 000, the original for the map
1:10 000 is obtained, which after providing it with title and legend is copied on to a
zinc plate. By a photographic reduction of the same base map to the scale 1:25 000, the
original for the publication scale 1 25 000 is obtained by combination of two reduced
sheets 1 12 500.
Apart from other purposes, the map >1:10 000 provides the data for the area measure-
ments on behalf of the Netherlands land use System, which is divided into 18 categories.
The reduction on dimensional stable film, scale 1:25 000, mentioned above, and
called the general diapositive, plays an important role in the next part of the cartographic
process and is often mentioned in this article.
This general diapositive is photographically copied on stabilene Y 466. Its image
produces a very clear and sharp guide for the engraving of the map 1 25 000. On this
map the road width has been exaggerated and a road Classification has been carried
out, in which the width has been standardized. For these standardized widths, double line
scribing needles are used. Along a straight edge or templet roads are engraved first, and
afterwards all the other details are to appear on the map in black.
In many countries special tools are used for the engraving of roads. Until now the Dutch Topo
graphic Service has obtained satisfactory results with some of those tools and in future it may be
possible to switch over to those devices. But the difficulty, encountered when double line needles
are' used, is that this kind of needle must always be held perpendicular to the direction of the
road, otherwise the width will not be constant.
With the scribing technique on plastic it is necessary to avoid both scratching of the base material
and any imperfect cutting of the coating. For in the latter case the engraved line will not be shown
in füll black when the negative engraving has been copied. In using a double line needle freehand,
the danger of scratching the base material is greater than when using scribing tools with three or
four supports.
When the engraving of the black line drawing (engraving black for short) has been
completed (as mentioned above) a diapositive is made photographically. In order to
obtain a guide for the engraving blue, the diapositive of the black is first photograph
ically copied, by contact printing, onto a new sheet of stabilene Y 466. The exposure
time, however, is very short. After this the general diapositive is placed in perfect
register with the same sheet of stabilene and also photographically copied but with the
normal, rather long exposure time. After development the image of the general dia
positive is a grey tint, while the image of the already engraved black part of the map
appears in füll black. On the guide thus obtained, with its colours of grey and black,
is clearly visible what already has been engraved and it is possible now to engrave the
blue line drawing (the grey guide) taking into account the exaggerated road width of
the black image. After the engraving of the blue map elements a combined diapositive
from the engravings 'black' and 'blue' is made. On a new sheet of stabilene Y 466
this combined diapositive is copied first, by exposing it briefly again. After this short
