Map type 
5,6 
100 000 
500 000 
7412 
Photomaps 
Pictomaps 
  
A1 (quick continuous revis.) 
A2( » cyclic » ) 
A3 ( » selective » ) 
B1 (partial continuous rev.) 
B2 ( » cyclic » ) 
B3( » selective » ) 
C1 (complete continuous rev.) 
C2 ( :» cyclic » ) 
C3( » selective ») 
  
  
% 3 
% 8 
% 20 
% 2 
% 3 
% 10 
% 5 8 a 
% 30 29 55 % 
% 22 17 18 % 
9% 
9 % 
9 % 
16 
28 
30 
  
  
  
  
  
  
where the C3 revision of the base map (scale 
1 : 2500 and 1 : 1250) is done by personnel 
permanently detached on the territory, for 
an imposing number of map sheets per year. 
c) As for the quantity of the revisions per- 
formed in different Countries and Agencies, 
very significant discrepancies are to be noti- 
ced. The differences are not only absolute 
(which is well intelligible, in connexion with 
the dimensions and the development of each 
Country and Agency), but remain very high al- 
so in the percentage of the total production, 
independently from technical development. In 
our opinion this fact means that while in some 
Countries it exists a « revision conscience » 
(i. e. the consciousness of the indispensable 
necessity of the revision, which leads to make 
ready and properly arrange the essential 
means to perform it), in other Countries the 
problem is far less considered (and I am sor- 
ry to say that my Country is among the second 
ones). Well, we hope that this « revision cons- 
cience » may grow and become universal. 
d) On the problem of deciding when the 
total renewing of a map sheet is or becomes 
preferable to a simple revision, only a few 
Agencies have expressed a firm and precise 
opinion. The situation is well synthetized by 
the answer of 142 (Geoplan A/S) : « the map 
is renewed when it is economical » : which 
is a little simplistic, but is not so different 
from what many other Agencies have expres- 
sed with many different more or less elaborate 
words. Almost all answers initiate by affir- 
ming that no fixed rules are used for this deci- 
sion ; many of them go on by informing that 
the decision is taken when major develop- 
ments dictate significant changes, or that it 
depends on the cartographic and geometric 
4 
qualities of the preexisting surveys, or on the 
degradation of the reproduction materials, 
etc. Many answers finally affirm that the 
decision of total renewing is taken when so- 
me percentage (which variates from 30 % to 
70 %, mean 60 %) of the map sheet area has 
to be completely revised ; or after 2-3 revi- 
sions ; or after 5-20 years. Only 522 (USGS) 
affirms that the decision is based on amount 
of change in one or more major features, 
rather than a proportion of total sheet ; and 
we believe that this is very wise. 
6. — The revision techniques 
a) About the sources of the revision in- 
formation, we must observe that the great 
mass is given by new aerial photos of the 
area to be revised ; very often there are also 
local elements and information collected from 
other organizations and agencies, preferably 
governmental or public ones. For the revision, 
black and white photos are almost exclusively 
employed, generally at the same scale as the 
original survey photos. 
For large scale maps, some Agencies uti- 
lize to a great extent terrestrial surveys and 
information ; among these there is 160 (Bri- 
tish Ordnance Survey), which keeps a large 
number of surveyors permanently placed on 
the entire national territory, whith the main 
task of maintaining up to date the basic 
1:1250, 1:2500 scale map, each one in his 
own area. We must notice also all the Ger- 
man Landesvermessungsamte and Agencies 
(200 to 209), which utilize revision informa- 
tion from many different sources expressly 
collected in the whole national territory by 
a unique federal bureau (The Topographic 
Information Service) deliberately instituted