Some discussion ensued on the relative merits of the instruments used for the interpretation, and whether there 
was a need for more sophisticated equipment. Other problems referred to included the desirability of having 
some forms of classifying the skill or ‘reference level” of interpreters; and, also, whether simple standard codes 
could be established to classify terrain forms. 
As far as the future programme is concerned, it was proposed that, in view of the large number of influencing 
parameters, the substantial tasks involved should preferably be dealt with by a working group, whose two main 
tasks will be to collect all existing information on the subject, and to promote experiments in an efficient and 
organized manner. The proposal to also consider the interpretability of orthophotos by laymen users was 
agreed upon, since, in effect, this only refers to the interpreter’s ‘“reference level". The suggestion that the 
whole subject of semantic information be referred to Commission E of the OEEPE was not considered feasible, 
due to that organization’s limited scope, but it was agreed upon that their co-operation should be enlisted. 
Monday July 31 1972, 10:45 
Map Revision Session 
Chairman: A.J. van der Weele 
Panel Chairman: W. Hofmann. 
Panel: G. Krauss, R. Verlaine, E. Huber, D. Proctor and M.M. Thompson. 
The Chairman opened the session with the remark that topographers have been making maps for many years 
now, and are thus necessarily becoming more involved with the important problems of map revision. The 
Invited Paper for this session, ‘Photogrammetric Operational Methods for the Revision of Topographic 
Maps" was then summarized by G. Krauss, followed by a brief description by M.M. Thompson of the map 
revision procedures employed by the USGS. 
The pressing problems of maintaining the 54,000 map sheets at the scale of 1:24,000 have resulted in the 
application of the following three revision procedures: 
(1) an interim revision procedure has been adopted in areas with limited changes, which are observed on 
photographs, and are overprinted in purple on the existing map without any field checks - the advantages being 
the shorter production time, the lower costs, and the fact that the purple overprints clearly define changes since 
the initial production of the map; 
(2) another procedure is the use of orthophotos, produced from high altitude photography, being printed 
on the reverse side of the maps, and having the advantage that maps can be up-dated at frequent intervals; 
(3) the USGS is at present investigating the feasibility of introducing an automated revision programme, 
whereby, with the new photography and the latest existing map as input, the maps will be digitized, profiles 
will be produced for the automatic production of orthophotos, and, finally, the orthophoto merged with the 
digital data for automatic plotting. 
The Chair of the session was then handed over to W. Hofmann for the panel discussion, which followed the 
introduction of the panel members. The replies to the problem of at what fundamental scales map revision 
should take place indicated that this is largely dependent on the organization of the mapping programme 
within specific countries. In Belgium, the basic scales of 1;5000 and 1:25,000 are revised simultaneously, the 
smaller scales being up-dated by generalization. In Great Britain, the different national series refer to different 
types of terrain, the large scale 1:2500 being revised continuously. In Switzerland, the revision scales are 1:5000 
and 1:10,000, whereas different scales are revised in the various West German states. There, attempts are being 
made to introduce the simultaneous revision of different map scales, in view of the time lags presently 
experienced with the successive revision of decreasing scales. Finally, the USGS principally revise the 1:24,000 
series in addition to their continuous maintenance of the 1:250,000 series. 
Most of the countries indicated that they would like to introduce a fixed cyclic revision programme, with urban 
maps being revised roughly every five years, but at present this only seems to be operational in Switzerland, 
with Great Britain having a continuous revision programme. 
In Belgium, West Germany and the USA, selective revision is carried out, in the latter case, based on the system 
of user demand. A brief discussion ensued on the type of revision executed, Switzerland reporting that they 
could never accept an interim revision system. In reply, it was argued that America is faced with the choice 
of either producing a preliminary map or no map at all, if they were to maintain the high standards.