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the Topographic Maps 1:25 000 and 1:50 000 are revised at 5 years intervals. In accordance with 
this cycle, fixed for a long period in advance, not only the necessary aerial photographs are taken, 
but also the cadastral offices are urged to present the corresponding revised basic map 1:5 000 at 
the fixed dates. These dates are established in accordance with the most important map users and, 
as far as possible, adapted to certain requirements. 
The extent of work mostly being very large and the time available for a complete checking 
always being too short, we must partially confine ourselves to consider only the most important 
modifications. For this reason we distinguish between three main groups : 
1) Complete revision (Correction B) 
The total map content is checked and revised. 
  
2) Partial revision (Single corrections N) 
In general, only modifications of special importance are taken into account. 
  
3) Editorial revision 
Only abstract information as name and boundary modifications are considered. 
For economic reasons the complete revision should be strived after and, at least, the whole 
planimetry should be checked and revised. 
4. - The Up- To-Dateness of the Map 
  
As to the up-to-dateness of a map in general, the following formula is applicable : 
MA = FZ/2 + BZ 
where: MA - Mean age, FZ - Revision cycle, BZ - Working time [3] . 
Consequently, the up-to-dateness depends on revision cycle and working time, which is 
the time elapsing between the ascertainment of modifications andthe publication ofthe revised map. 
The up-to-dateness of a map can therefore be improved by reducing the cycle and the working 
time. As the reduction of the working time has a full effect, the reduction of the cycle, however, 
has only half the effect, every endeavour should be made to reduce the working time. 
Basing on this knowledge, we have succeeded inthe last years, by improved working 
methods and concentration of the working process, in reducing working time, which partly amoun- 
ted to 3 - 4 years, to.nearly one year. Thus we have considerably improved the up-to-dateness of 
the map in spite of the fact that the cycle remained unchanged, e.g. 6 years. Consequently the 
mean age of the map which amounted to 6 and 7 years respectively has been reduced to 4 years. 
5. - The Data of Revision 
  
For the greatest part of the Federal Republic of Germany, in the meantime, a topographic 
basic map at a large scale is available. Consequently, the Topographic Map 1:25000 has become 
a derived scale for map remaking, that means, that for a remaking of individual sheets, the 
drawing of the Topographic Map 1:25 000 is no longer directly mapped or plotted photogrammetri- 
cally, but that it will be derived from large-scale basic maps. 
  
The revision of the Topographic Map 1:25 000, however, ist mostly based upon a directly 
plotting of aerial photographs. Indeed, this is performed in very different ways, depending on the 
terrain and instrumental equipment available. The existing basic maps, as far as revised, will 
be used in addition, as well as other large-scale data, as e. g. that of road construction offices. 
From these data particular information is taken as e. g. classification of roads or changes of 
names, not shown on the aerial photograph. But for the most part, the aerial photographs taken 
at regular intervals constitute the most important documents for the revision of the Topographic 
Map 1:25 000. 
  
  
Only one federal state tries to revise at first the corresponding sheets of the Basic Map 
1:5 000 and then to revise basing on these documents the sheets of the Topographic Map 1:25 000 
consistently. There the local cadastral offices are charged with the revision of the basic map. For 
a revision of the Topographic Map 1:25000, which is exclusively based on the basic map it is ne- 
cessary to have capable local offices as wellas a very careful organization. And such conditions 
are only seldom existing. 
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