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.
