Guerra, Francesco 
  
e the meaning of the sign, 
and having proven that the signs are 
contained in the texture, in other 
words, in the attributes of he image, 
it is necessary to ask if it is correct 
to distort the aspect of a map to the 
point of making it unrecognisable. 
If it is true that the semantic content 
is drawn from the change of the 
geometric support, it would be 
necessary to investigate if the 
metamorphosis of the signs 
implicates a change in their 
meaning. It is necessary to 
understand if the presumed 
indifference of the texture is true 
with respect to the geometry that figurel. Superimposition of the geo-referenced images before and after loca 
would assume a sort of invariance transformations. The best superimposition of the two images can be seen in the figure 
It can be proven, in a pragmatic at right with respect to the left one. 
way, that the question does not lead to an absolute definition, but is relative to the “amount of change”. 
Commonly, if the image of the map has changed little with respect to the initial condition and the new image is 
acceptable, the operation is correct (as in the case of the photoplane); if on the other hand, the image is unrecognisable, 
or in any case unacceptable from an “aesthetic” point of view, the operation would be considered incorrect (see the 
examples of the figures illustrated in this chapter). 
Obviously, the distinctions regard the typology of the map as well: for the modern cadastral maps, the questions will be 
different from an Atlas of the 1500s and different still from those that concern historic photoplanes. 
  
  
  
  
  
  
figure2. An example of deformation introduced after a geo-referencing transformation 
2 HISTORIC CARTOGRAPHY 
Historic cartography is surely an area where the questions made in relation to the referencing-transformation assume a 
great deal of importance. 
Although it is always difficult and perhaps even incorrect to generalise, historic cartography does present some common 
characteristics, such as: 
e an undefined reference system, 
e an approximate projective system, 
e an uncertain metric content, 
e a semantic content which is difficult to interpret. 
These characteristics in the maps from different time periods are encountered in greater or lesser measure, and as has 
been proven time and time again that it is imperative to make specific considerations when faced with each different 
map. 
  
340 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000.