GVII-6 (Sup.) 
$0 elements always indicate differences and similarities in 
soil conditions. 
This so-called "pedological photo-analysis” as practiced 
in the Netherlands leads to a thorough study of the terrain 
and differences of soil conditions before actual field work 
starts. On the so-called "photo-analytical” map many im 
portant boundaries can already be indicated, and a preliminary 
classification of the mapping units becomes possible. By 
control and checking in the field, this photo-analytical map 
set up for soil survey, land-use planning or soil conservation 
purposes is transformed into a real soil map, land classifica 
tion or land capability map. In this way much time is saved 
on the wearisome job of plotting the boundaries in the field, 
so that more time is left for terrain studies of profiles 
and conditions. 
This method is especially important for semi-detailed 
mapping (Is$0,000). In reconnaissance surveys (Is 100,000 - 
Is 200,000), the pedological photo-analysis can be combined 
with direct photo interpretation. Under special conditions 
as regards the photo material, photo interpretation is based 
on a method of interpolation. Key areas are first thoroughly 
analyzed on the photographs and mapped in the field in order 
to establish the regular relationships between soils and their 
appearance on the photographs. For schematic mapping (Is300,000 
and smaller) only a few representative areas are analyzed and 
mapped. The information collected in these areas, together with 
general knowledge about soil condition and their appearance on 
the photographs is extrapolated in an interpretation over the 
rest of the terrain. The result is not more than an ex 
ploratory soil or land classification map. 
Various areas have been mapped according to the above 
described methods as developed in the Netherlands. As the 
most important areas are mentioned parts of Clark County in 
the USA, Merauke area in Dutch New Guinea, the Ghab valley 
area in Syria, the Methahara area in Ethiopia, the Hammar 
Lake area and Massayeb area in Iraq and the Ngatapa area 
in New Zealand, the last area especially for soil con 
servation purposes. 
In Switzerland, in the agricultural domain, the Fed 
eral and Cantonal Government authorities and subordinate 
instances are among the most active users of aerial 
photographs. Melioration programs, e.g., to be submitted 
for study and arbitration, though delineated on large 
scale cadastral plans, come more and more accompanied