to this purpose. 
Only a few Agencies (the Mil. Geographic 
Institute of Argentina, and the Canadian 
agencies) already utilize space data and ima- 
gery for the revision of their small scale 
maps. Various other Agencies have studies 
and experiments on this matter, or deem. 
them desirable. 
b) The majority of the B and C type 
revisions is executed by regular photogram- 
metric plotting, based on regular control 
points or at least on control points desumed 
from the preexisting map. Only the 22 % 
of such revisions is done by other methods 
(terrestrial surveys, use of rectified pho- 
tos or orthophotos, use of special instru- 
ments, etc.). It is to be noted that only 
10 Agencies, that is the 20 %, actually 
use orthophotos for map revision, while 23 
(45%) use simply rectified or unrectified 
photos, and 8 (16 96) use the technique « pho- 
to versus map » by special devices, general- 
ly simple and not expensive, like Zoom Trans- 
fer Scope, Sketchmaster, Stéréoréviseur, etc. 
These are, at present, the only instruments 
which are born exclusively to make revision ; 
in my opinion, something more should be do- 
ne, and more rigorous devices specially con- 
ceived for revision should be built: because 
the above said instruments — particularly if 
monocular — and also some simplified opti- 
cal stereoplotters not always have given satis- 
factory results. I guess that a new good revi- 
sion instrument could find a prompt com- 
mercial disposal, and I beg the buiding Firms 
to take this remark in good account. 
c) Generally the larger scale maps (1:1000 
to 1:50 000) are directly revised, while the up- 
dating of smaller scales is derived from these 
by generalization and other cartographic ope- 
rations. Nevertheless, there are some Agencies 
which do not revise their large scale maps, 
due to shortage of personnel and means, while 
they revise their small scale maps; e.g. 021 
(Military Geographic Institute of Argentina), 
which starts its revisions from the 1:250 000 
scale maps, with information limited to space 
sources and other data from various Agen- 
cies which deal with routes, demographics, 
politics, etc. A Canadian Agency (082, Alberta 
Energy and Natural Resources) literally states 
that « a constantly up to date proper map revi- 
sion would be tremendously expensive and 
possibly not justified, due to the area involved 
(245 000 square miles). As result, many carto- 
graphic principles are ignored in an attempt 
to provide up to date maps with the funds 
that are available.» In my opinion this is a 
very wise principle: it is far better to pro- 
duce now a second-rate revision than to pro- 
duce later — and often too late — a perfect 
revision. I would like to add « whatever be 
the territory involved ». 
d) The technique by which the new revi- 
sed features are reported onto the preexisting 
maps are the most various; they go from a 
simple overprint in a strong colour (red) of 
the new lines on the old map, even without 
erasing the old lines, to the most complex and 
sophisticated automated editing operations. 
In many cases, the procedure applied is quite 
similar to the production procedure, in other 
cases it is different. 
Anyhow, we want to point out 
that there is a strong cost and time difference 
between the techniques applied in the revision 
of single colour or multicolour maps ; under 
this point of view, single colour maps are far 
preferable. 
e) The diffusion of the revised maps is 
generally effected by the same means as the 
original map. For large scales there is a pre- 
valence of non-offset printing (diapositive or 
negative films, diazo or dialine copies, bro- 
mide photomaps, etc.), while for medium and 
small scale maps the offset printing is gene- 
rally employed. Microfilms are also used by 
160 (British Ordnance Survey) for the 1:1250, 
1:2500 basic scale revised maps. 
5. — The revision accuracy 
a) A very important item considered in 
the Questionnaire is the accuracy of the revi- 
sed maps. A large majority of the answers 
(76 96) indicates that after each revision the- 
re is no accuracy decrease, or a very little 
one (0.2 — 0.3 mm); a notable percentage 
(13 96) yet indicates that the accuracy wor- 
sening is not over 0.4 mm; only 4 Agencies 
(081, 260, 400, 522) deem uncertain or unknown 
the accuracy decrease due to the revision. 
There are even 3 Agencies (400, 480, 520) 
which are of the opinion that in some cases 
the accuracy of a map may increase after a 
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