the best solution is a combination of production speed 
and low costs — this is the case with analytical aerial 
triangulation for mapping purposes. Analytical aerial 
triangulation over large areas (or, more generally, of 
large blocks of photographs) eliminated the difficulty 
that often was referred to as a "bottleneck" in map- 
ping operations. When supported by such airborne 
methods as the Radar Profile and Aerodist, this meth- 
od permits to determine rapidly, the necessary contro! 
points under the most difficult circumstances. Please 
refer to specialized publications in this regard [2, 3, 
4]. I would like, however, to mention en passant, 
that the laser type of Profile Recorder is in an ad- 
vanced experimental stage [5]. There is no doubt 
that this new technique, which promises astonishing 
performance, will further equip photogrammetry with 
à powerful tool for the task of mapping large and 
remote territories. 
Orthophoto maps 
  
The intent to develop an automatic mapping 
technique, pursued from the earliest days of photo- 
grammetry, found its fulfillment in the orthophoto 
technique. This is probably one of the most remark- 
able events in mapping history. Yet, it is seldom re- 
cognized as such partly because of the novelty of the 
product. The orthophoto map is vastly different from 
the conventional map: the latter is a symbolized pic- 
ture of an abstract of the earth's surface, whereas the 
former is its geometrically correct, true photographic 
picture. The content of the conventional map is de- 
cided upon at the design stage, whereas the ortho- 
photo map, in principle, includes all the cartographic 
information of the terrain, and it is up to the user to 
interpret and to select information according to his 
need. 
Some mappers and cartographers have the ten- 
dency to reject spontaneously the orthophoto product 
as a new concept in mapping because the orthophoto 
map does not meet the classic definition of a map. 
Conversely, it could be reasoned, that only because 
an orthophoto is sufficiently different from the con- 
ventional map is there a chance of a far-reaching so- 
lution, presenting exceptional advantages and possi- 
bilities from the standpoint of production. 
Leaving this question aside, let us analyze the 
new vistas open to mapping and to small scale map- 
ping by the orthophoto approach. There are some im- 
portant features of this technique that must be con- 
sidered from the outset to make the discussion mean- 
ingful: 
— Contouring and relief shading is obtained auto- 
matically and simultaneously with the ortho- 
photo process. Resulting time and cost savings 
are of the utmost importance, not only in the 
ordinary sense, but also because they allow new 
approaches to mapping projects of particular 
urgency or of a temporary nature. 
— Orthophoto technique offers a new approach to 
mapping in general, including conventional map- 
ping, where a linedrawn map is the final pro- 
duct. The development of the stereo orthophoto 
should be mentioned particularly in this connec- 
tion. 
As I tried to explain on previous occasions, there 
is an obvious relationship between the tool and pro- 
duct: They should be permitted to act on each other 
until an optimum solution is achieved. Any rigid, 
preconceived ideas or specifications introduce undue 
difficulties ^nd slow the progress. It is important, 
when considering the orthophoto technique as ^ new 
mapping tool, that we maintain this flexible attitude. 
Contrary to the opinions advanced by some ma- 
nufacturers of orthophoto equipment, use of ortho- 
photo maps for scales smaller than 1:25,000 entails 
certain difficulties which definitely make it not as 
advantageous and straightforward as in the large- 
scale range. This is simply because many details cease 
to be recognisable at smaller photographic scales and 
thus require symbolization. Therefore, the question 
arises: What is the advantage of using the orthophoto 
approach for small-scale mapping (1:25,000 and 
smaller) if extensive symbolization is necessary? 
From personal experience I would like to make the 
following observations: 
Unless the photographic background is undesir- 
able (which in some instances is the case) there is no 
convincing argument why symbolization should not 
be added io the orthophoto manuscript. Most often 
the ch>racteristic features of the terrain can better be 
presented by an adequately processed orthophoto map 
than by using the conventional technique. This ap- 
plies particularly to less developed areas, where the 
need for mapping is urgent. In such areas, there are 
relatively few artificial details requiring symboliza- 
tion; the greater part of a map consists of natural 
features such as topography (contour lines), bodies 
of water and vegetation. In this respect, there is no 
doubt that the orthophoto technique offers a superior 
form of cartographic presentation. In addition, the 
basic sheets are obtained simultaneously and at great 
speed. 
If, however, a conventional line-drawn map is 
required, the orthophoto technique [6] may present 
an attractive and efficient solution. The usual ortho- 
photos, the contour line sheets, and the shaded relief 
sheets of the land to be mapped are produced in one 
scanning operation. Then the orthophoto manuscript 
is observed stereoscopically together with the enlarge- 
ment of the second photograph of the stereopair (or 
its contact copy, if a special observation device is 
available). By this mode of observation, superior in- 
terpretability of the viewed "stereomodel" is achieved 
in a manner very similar to that on stereoplotters and 
the details that must be symbolized are drawn or 
scribed. 
In this regard, a very special note must be made 
of the stereo-orthophoto developed at the National 
Research Council of Canada [7]. In this novel tech- 
nique, a "stereo-mate" of the orthophoto is produced, 
preferably in the same scanning process as the ori- 
ginal orthophoto. The stereo-mate is a rectified photo- 
graph, similar to the orthophoto, with the difference 
that the horizontal parallaxes of terrain points are 
proportional to the elevation differences. The im- 
portant feature of this approach is the fact that the 
vertical parallaxes between the orthophoto and the 
orthophoto-mate have been eliminated in the scan- 
naailMli