CIPA 2005 XX International Symposium. 26 September - 01 October. 2005. Torino. Italy 
GEOREFERENCING THE HISTORICAL MAPS OF ROME BETWEEN THE 
SEVENTEENTH AND EIGHTEENTH CENTURIES 
V. Baiocchi 3 , K. Lelo b 
a DITS - Area Topografia, Università degli studi di Roma “La Sapienza”, Via Eudossiana 18, 00184 Roma. ITALY - 
Valerio.baiocchi@uniroma 1 .it 
h CROMA (Centro di ateneo per lo Studio di Roma), Università degli studi di Roma Tre, Via Ostiense 139, 00154 Roma, ITALY - 
lelo@uniroma3.it 
KEY WORDS: Rome, historic cartography, georeferencing, GPS, GIS 
ABSTRACT 
Historical studies often need to consider both geographic and temporal aspects of the analysed phenomenon. At present, 
Geographical Information Systems (GIS) can provide historians with a series of extremely useful tools for analysing the territory and 
its temporal transformations. As already known, historical maps may lack of geographic reference systems or may be expressed in 
systems which are substantially different from the contemporary ones. The georeferencing of this kind of documents can be 
performed through the identification of points remained unchanged over time, univocally recognizable in the historical map as well 
as in actual cartography and/or in the terrain, to be used as tie points. This procedure bears limits of metric precision, but in most of 
the cases results to be the only one applicable. In this paper we analyse the procedure of georeferencing historical cartography by 
means of a GPS campaign of measurements, and further on, investigate the conditions of comparison with recent small scale digital 
cartography, in order to evaluate its eventual use for georeferencing the historical maps. 
1. INTRODUCTION 
This paper refers to the on going experience of CROMA 
(Centro di ateneo per lo studio di Roma - University Roma 
Tre), for the construction of a GIS based Historical Atlas of 
Modem and Contemporary Rome. 
The process of georeferencing historical cartographic sources is 
very complex and demands, in first place, a careful evaluation 
of the characteristics of every single map. The techniques of 
pre-modem cartography vary from the symbolic modality of the 
XIII th century representations, to the plastigrafic three- 
dimensional modality of the perspective views (a volo 
d’uccello), very much appreciated between XVI th and XVII th 
century, and finally to the iconographic two-dimensional 
representations, gradually evolving in terms of geometric 
precision from the XVIII th century. It is clear that maps grouped 
in the third category -which method and instalments of 
measurement differ from the contemporary ones principally in 
the phase of densification - are the only ones that can be 
georeferenced. However, these cartographies, although of 
remarkable precision considering the early date of production, 
often present metric eaors superior to those conventionally 
accepted. The GIS techniques of calibration, georeferencing and 
transformation of projection, enable the comparison between 
historical and actual cartographies, permitting to reduce the 
effects of deformation of the media supports (paper) and those 
due to the different systems of representation and measurement. 
The work is articulated in three principal stages: 
study of the historical cartographic sources, paying 
particular attention to the techniques of measurement 
and to the overall metric quality; 
georeferencing of two "sufficiently accurate” 
historical maps using a network of tie points deriving 
from a GPS survey; 
evaluating the possibility of using last generation 
digital cartography for georeferencing historical maps, 
and as term of comparison for studying of the 
geometric variations of buildings. 
2. METHODS AND PROCEDURES 
2.1 The historical cartography 
The Topographical Plan of Rome, published in 1866 by the 
Direzione Generate del Censo, is the cartographic source at the 
basis of the first digital thematic cartography expressed in 
geographic coordinates of the Historical Atlas of Modern and 
Contemporary Rome. The choice of the source is based mainly 
on the fact that this map corresponds to the city in 1870. It is the 
last map, drawn with an acceptable level of accuracy, 
representing the city before the deep transformations that came 
up after the Unification of Italy. Moreover, the choice of a late 
1800's cartography allows better conditions of comparison with 
the contemporary cartography initially used as reference for the 
georeferencing procedure. Bibliographic and archive 
investigations have been carried out in order to obtain 
indications on the modalities of production of this map and its 
degree of accuracy from the cartographic point of view. This 
has guided us towards a series of considerations regarding 
previous cartographies that served as bases for its compilation. 
In fact, the map is an up-to-date version of a previous edition of 
1829, compiled on the bases of the cadastral map (1818-22). 
Both maps consists of a reduction in scale 1:4.000 of the 
original map of the city cadastre in scale 1:1.000. Concerning 
the techniques and modalities of the topographical survey of the 
cadastral map, which is at the basis of almost all the maps of 
Rome between 1820 and 1870 (until the realization of the first 
IGM cartography, after the Unification), the archive sources do 
not offer satisfactory explanations. It appears that the roman 
architects Salvi e Palazzi, members of the S. Luca Academy, 
charged of the project by the Reverenda Camera Apostolica, 
suggested as an alternative to a brand new measurement 
campaign of the city, to take advantage of the Plan of Rome of 
1748, by Giambattista Nolli, “introducing all the necessary 
corrections and integrations where [...] any transformation 
might have occurred” (Ruggeri, Londei, 2000). Work would 
have then begun at the drawing board by enlarging Nolli’s work 
(approximately 1:2900) and bringing it to a 1:1000 scale, a 
procedure that would have taken approximately four months, 
and continued with a longer and more complex phase of field 
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