Analytical methods and new tecnologies 
for geometrical analysis and geo-referenced visualisation of Historical Maps 
Caterina Balletti, Francesco Guerra, Carlo Monti 
DIIAR Dipartimento di Ingegneria Idraulica, Ambientale e del Rilevamento 
Sezione Rilevamento - Politecnico di Milano 
P.zza Leonardo da Vinci 32 - 20133 Milano 
ISPRS - WG VI/3 - WG IV/3 
KEY WORDS: historical cartography - plane transformations - geometrical analysis - geo-referecing - software 
ABSTRACT 
The need and desire to produce instruments for the understanding and fruition of the historic cartography are born from 
these considerations: the understanding of the contents of the old maps is undoubtedly difficult just because, on one 
hand, it assumes that there is an understanding of general cartography; on the other, a knowledge of the interpretative 
codes from the time period and the atmosphere of their production. The result made be a difficulty in their reading on 
the part of the general public both of the geometric content and the semantic content. 
The fundamental idea is that of allowing anybody to extract information from the historic cartography, rendering more 
transparent the complex yet necessary operations of geo-referencing. 
The preliminary remark is to recover the metrical content in historical maps (particularly perspective views of towns of 
XV-XVI century) using analyses which lead to a definition of a methodology for the quantitative analysis of historical 
cartography. 
This implies to use procedures that treat of global and local transformations. 
The plane transformations allow for the deformation of a map in a way which makes them assume the metric and 
geometric content of another reference map. This leads to the manipulation of the map being studied which 
consequently is subjected to warping, at times so great as to totally distort the original aspect. The price to pay for 
making a historic map metric according to modern parameters is that of losing some of the semantic content of the map 
itself. This situation is acceptable if it is then used for didactic and research purposes, but not if the map is being used by 
someone who wants to reads the map in its original form. 
How can we join the desire to extract geometric information from a historical map while always maintaining the original 
aspect? The computer and the “infographic" come to help us: the solution is that of using software capable of putting in 
correspondence bi-univocal and visualising, interactively and in real time, a current numerical map of reference and a 
digital image of the historical map. The 2W software presented in this paper responds to these characteristics. 
For years, the historic cartography has been a subject of 
study by the historians and therefore, it has been 
considered as an archive document, a testimony of a 
certain period in the history of a territory, of a city. The 
study initiated and proposed in this paper faces, rather, 
the historic cartography according to an approach which is 
typical of the current cartography: extract territorial 
information which has been spatially referenced. 
The historic cartography is surely a field in which the 
questions relating to the referencing assume great 
interest. It presents some common characteristics such 
as: 
• a non definite reference system, 
• an approximate projected system, 
• an uncertain metric content, 
• semantic content difficult to interpret. 
Such characteristics in the maps and charts from varying 
eras are found in greater or lesser measures, and 
consequently, it is necessary to make specific 
considerations when faced with each and every individual 
map. 
The fact remains that, in general, the assigning of a 
correct metric support is very important for the use in 
cartography, not only as a document for the archives, that 
is, of a qualitative nature, but a true cartography from 
which to extract quantitative information. 
An idea that must guide and propel in this direction is that 
it is important to keep in mind that these charts have been 
created as charts, that is, with an operative and practical 
purpose, and that they were used as such. Perhaps the 
concept of metrics has changed, or more simply, the 
acceptable accuracy threshold has changed over the 
years. 
A case study: Jacopo de' Barbari and the City of 
Venice in 1500 
The study presented has concentrated primarily one the 
perspective views, which, if on the on hand, these have 
the advantage of being easily understandable in so far as 
the perspective is among the methods of representation 
which is most widespread, on the other hand, it is in fact, 
not measurable, if not by resorting to tricks which 
implicate a deep understanding of the descriptive 
geometry. The choice to use the perspective views of 
Venice by Jacopo de’ Barbari was motivated not only by 
celebratory reasons (in the year 2000 it will be 500 years 
from the first year of the publication of the map), but 
especially for the geometric and cartographic 
characteristics of this map that represents the most 
exciting example of the new method of representation of 
the city based on perspectives. For the actual reference 
cartography for referencing, the photoplane of Venice was 
chosen. 
The main problem was to understand whether the 
perspective construction of the work was quite rigorous, 
based on existing plans and charts, or whether it had 
been produced by a preliminary survey campaign, and in 
this case, which instruments and methods had been used.