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Firstly: it is impossible now to go beyond the lines with the black ink; the selected
areas between the etched lines are simply peeled off. Consequently, the accuracy and
quality of the map are improved. Secondly: the negative method is quicker than the
positive method.
c. New materials
Plastic materials such as astralon and astrafoil belong to the polyvinyl group. The
new plastic materials used nowadays are polyesters. The polyesters have the advantage
of a greater dimensional stability. Their thermal expansion coefficient is about one
fourth of the thermal expansion coefficient of the plastic of the polyvinyl group. This
high stability is a most important property in the cartographic process. It will be clear
that a map's quality is determined by the exact fitting of colour areas within the lines
(-registering)Although polyester products are much more stable than polyvinyl pro
ducts, they still do not have absolute stability. In choosing glass the ideal is obtained.
Not only in regard to stability but also in the quality of engraving. The harder the base
material, the higher the quality of the engraved lines. On the other hand there are the
disadvantages of glass: the risk of breakage, the great weight, the difficulties in trans-
port from one department to another, the more elaborate manipulations in photo-
graphing and copying and moreover the heavy load in the archives. Nowadays one finds
on one side grim supporters of the use of glass, among whom Swiss cartographers are
to be mentioned, on the other side supporters for polyester materials, among whom
American cartographers take the first place. Those willing to give up something of the
maximum in the beauty of the map for a quicker and more manageable cartographic
process choose plastics. In other words, on one side are those who have used polyvinyl
products for some decennia and who have switched over to the better polyester materials
easily, and on the other side one finds those who practised copper engraving and stone
lithography and switched over to glass as a base material. This point is open to extensive
discussion. Cartographers or cartographic institutes have to make their own choice as to
the method to be applied. After many and extensive experiments of every kind the
Topographie Service has also made its choice. Without reporting its considerations it
may be mentioned that the Topographie Service has chosen for the polyestersheet the
'stabilene of Messrs Keuffel Esser, U.S.A. as a base material.
'Stabilene' is a group name, given by this firm to all its films, about 40 different
ones in all. These films bear different numbers and are respectively used for scribing,
Stripping, copying and photographing as well as for drawing with pencil and ink. Thus
one has the command of a wide choice while the advantage of a single base material is
that all cartographic Operations are made with one and the same material. The name
of this polyester base material, used for the produetion of the various stabilene films
is 'mylar'.
Th e new cartographic process at the Topographie Service
The Dutch topographic map is, for most flat parts of the country, based on rectified
air photographs. For the hilly parts of the country the maps are composed by means of
stereoplotting machines. The rectified airphotos are produced on dimensional stable film
on the scale 1 12 500. Sections of these airphotos are cut out very precisely along
connecting lines between the control points and stuck onto a blank sheet of stabilene
(no 464) on which the corresponding control points have been plotted previously with
the aid of a coördinatograph. Then some parts, mapped with the aid of the stereo
plotting machines, are cut along four control points and stuck onto the blank sheet
stabilene too. Next, this mozaic is reproduced on a sheet of stabilene Y 466 (diazo-
