by the combination of two colours hardly admits a clear definition of features, in particular, when 
small elements are concerned. In order to attain the required accuracy, it is necessary to work 
at the enlarged scale of 1:10000. Furthermore, some difficulties arise to tune the colour of the 
map in such a way that it differs clearly from the anaglyph. These difficulties are avoided when 
instruments are used, in which a subjective, optical model is produced which can be observed by 
means of a good optical system. Some organizations work with the Wild Aviograph B8. With this 
instrument, wide-angle lens photographs are used at 1:36 000 scale, and only the principal line 
elements, as e. g. road centre lines are plotted at 1:25 000 scale. This instrument allows, for the 
internal plotting, magnification from image to model extending from 1.4 to 2.1 times. A brown 
print of the map serves as support. Details as e. g. the individual buildings are mostly inserted 
according to this base with sufficient accuracy subsequently to the plotted line elements, because 
photo and drawing scale are small. With this working flow the plottings of the aerial photographs 
are at first pencilled on a brown print 1:25 000. This brown print is, together with the correspon- 
ding aerial photographs, the base of the subsequent field checking. After field checking, this pencil 
drawing has to be prepared as revision manuscript, which is the base of transferring the modifi- 
cations into the originals. 
In the State Survey Office of Northrhine-Westphalia the Planicart E 2 of Messrs. Zeiss has 
proved to be especially successful in the revision work of the Topographic Map 1:25000. For the 
internal plotting the instrument has the magnification factors of from 0.3 to 3. 5 from photograph 
to model. The photo scale, however, does not only depend on the plotter but also on the sheet line 
system of the map and, in particular, on the smallest elements which have still to be interpreted 
at this scale. We have performed several smaller tests with wide-angle lens photographs at 1:18 000, 
1:24 000, 1:35000, and 1:64 000 scales. The scales of 1:18000 and 1:24 000 are not economic because 
of the great number of models. Scales smaller than 1:50 000 can still be plotted successfully with 
the Planicart, but smaller elements are frequently no more exactly interpretable. Consequently, 
the expenses for fieldwork increase. Photo scales of about 1:35 000 have proved to be especially 
successful for our revision of the Topographic Map 1:25 000 with regard to technology and economy. 
About 8 models form one map sheet (~ 125 km2). On a light table the modifications are included 
on, the transparent copy of an enlargement 1:10000 (1/4 of a sheet of the Topographic Map 1:25 000). 
The map being observed by a magnifying glass with the same magnification (6 times) as the model, 
no adaptation of the eyes will be necessary, when they change looking from the model to the map or 
from map to model. Furthermore, with such a ratio of magnification, even the smallest elements 
are reliably interpretable. Field checking could be reduced from 15 days to 3 - 5 days for each sheet. 
It is advantageous to determine the classification of new roads, eventually by consulting the ser- 
vices concerned. Immediately after completion of plotting, it is possible to begin with the carto- 
graphic work of correction and simultaneously with field checking. In general, the field check 
only results in minor supplements, which have been neglected in plotting or which could not be 
interpreted unequivocally. 
Since displacements occur already at 1:25 000 scale and since the sheets from the very 
beginning have no uniform planimetric accuracy, the supplements must be fitted into their direct 
neighbourhood. With the Planicart it is possible to slightly displace (0,6 x 0,6 cm) the model. Thus, 
the map to be revised, can be fastened on the light table, and the supplements can in each case be 
fitted correctly into their environment. This device favours the ready flow of plotting to a consi- 
derable extent. 
In the last year Messrs. Zeiss, Oberkochen, produced the Planitop 5 for plotting at smaller 
scales and for map revision. This instrument has magnification factors of from 0.5 to 1. 5 for wide- 
angle lens photographs. In a test, aerial photographs for a sheet of the Topographic Map 1:25 000 
have been plotted by means of this instrument at 1:25 000 scale. The same photographic material 
had already been plotted with the Planicart E 2 (wide-angle lens photographs 1:33 000). The result 
of the plotting has been compared with the Planicart plotting. A very good conformity has resulted. 
Only minor parts, probably because of the smaller plotting scale, are lacking in the Planitop plot- 
ting. Because of the smaller plotting scale, however, the plotting has to be reworked to a small 
extent, so that it can be used as unequivocal manuscript for field checking and for the revision of 
the Topographic Maps 1:25 000 and 1:50 000. 
It some improvements, as e. g. a large magnifying glass will be installed in this instru- 
ment, the Planitop will be an excellent instrument for revision work at all medium and small photo 
scales, for which the use of e. g. a Planicart would be too expensive. 
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