database structure and map registration - Laboratorio di Geomatica

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

An open-HGIS project for the city of Parma: database structure and map registration Nazarena Bruno, Giorgia Bianchi, Andrea Zerbi, Riccardo Roncella Dipartimento di Ingegneria Civile, dell’Ambiente, del Territorio e Architettura (DICATeA), Università degli Studi di Parma

Abstract The observation of the structure of the city and its inhabitants, and how such system evolves in time, is essential in almost all land planning and urban development activities, as well as in any historical study. Historical GIS in the last decade proved to be one of the most promising frameworks, that can provide innovative tools and methodological approaches in this field, allowing new research perspective and concept in many fields. The paper describes the early stages of the development of a HGIS that considers different historical periods of Parma (Italy), with particular attention to cadastral documents and associated census data. These data are gathered from the main cadastres of the city: the Sardi Atlas of 1767, the Bourbon Cadastre of 1853, the PostUnitarian Cadastre of 1901 and the Cadastre of 1940. Other social statistics, conserved in the local communal and state archives, such as census reports, building permits, deeds, transfer of property, wills, etc., were considered in the project, leading to a quite complex database structure. In the hope of making the HGIS as flexible and scalable as possible, and to make the system usable to the widest spectrum of users, an open-source database architecture based on Postgresql/Postgis has been developed. The paper provides information about the database structure and the map registration stages, with particular reference to the first historical period considered in the project, based on the Sardi Atlas (drawn in 1767), which can be considered as the first parcelgeometric cadastre of Parma.

Keywords Historical cadastres, GIS, georeferencing, open-source, data-driven, image registration

1 Introduction The analysis of the city from many points of view, has always been important for historians of different disciplines. The observation of the structure of the city, its transformations and inhabitants that live in it, can provide an idea of society as well as architecture or urban structure. Therefore, knowing the structure of the city and interrelating it with its inhabitants can reconstruct the image of the society and the social and economic dynamics. To this aim, the analysis of cadastres and censuses is very important because these documents can be considered as main sources for knowing urban, 189

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

architectonical and demographic structure of the city. Moreover, the investigation of these documents is particularly significant to identify the forms of land use, urban structure, pre-existences and distribution of the property. Cadastres became privileged sources of territory knowledge in the Eighteenth century, when their realization became systematic in several Italian regions and the principles, which govern their structure still today, were identified. They included maps, based on topographic surveys, which showed the individual parcels. Each parcel was then included in a register containing information relative to its owner, type of crop and annuity. The paper will describe the first activities of a scientific project for the development of a Historical Geographic Information System (H-GIS or HGIS) of the city of Parma (Italy). In its very early stage the main purpose of the project was to provide a multi-user, low cost, information system for historians as a support for urban development studies. Now a further improvement of the project, addressing all the cartographic sources (up to modern age) and historical statistics (census reports, building permits, deeds, transfer of property, wills, etc.) preserved in city archives, that can provide thematic data to a wider range of user (e.g. architects, land planner, researcher, etc.), is in progress. The city, in fact, thanks to the creation in 1767 of its first geometric-parcel cadastre, known as Sardi Atlas (from the name of the cartographer Gian Pietro Sardi who drew it), took part in this first phase of national cadastral survey and was among the first cities that adopted a modern cadastre. In spite of the undoubted importance of documentary sources for historical city knowledge, in general their direct consultation is often difficult and very expensive in terms of time and effort in research. This because of problems related to conservation, lack of copies and reduced circulation, which limit the use of documents. To overcome these difficulties, computer technologies make new tools (above all GIS) available today for the analysis of historical data. Even if there is a difference between the original source and its digital reproduction, today digital scans of maps and documents and informative systems based on historical data are increasingly widespread. On the other hand, relational databases allow, in a much simpler way, not only historical investigations related to the single historical period (synchronic analysis) but also to different historical periods (diachronic analysis) in order to know the urban evolution in time. Despite the irreplaceable value of the original source, the information system aims to reproduce the documents in digital format, without distorting their structure and contents, in order to broaden the number of users and improve the research techniques thanks to the computer. Whilst in the late ’90 the growth of HGIS was slow and episodic (Gregory & Ell, 2007), from the very beginning of 2000 the scientific community developed a growing interest in such topics (Knowles, 2002). In many works one of the main features that make HGIS attractable for a wider range of scholars and researchers is an easier consultation of archival documents, thanks to the possibility also to visualize on a map information that are not spatial. For example in (Gauthiez et al., 2009, 2014) a HGIS for the city of Lyon (France) is described. The project, started in the late ’90, in based on the spatial 190

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

localization of several buildings described in archival documents, in particular the building permits given from 1617 to 1763. The maps used as base for the spatial reference belong to the 1745 to 1830 period, with particular regards to cadastral maps of 1830. Another project (Gregory et al., 2002), involving a more extended territory and a bigger amount of documents, is the GBHGIS realized by the University of Portsmouth on the whole Great Britain territory, since 1994. The original work was entirely focused on historical statistics: census reports, data on births, marriages and deaths, and on unemployment and poor law statistics. The data have been related to digital maps. Because the data had an high variability in time, a sequence of static maps in this project were not created, but each datum is date-stamped with a start-date and an end-date. An interesting HGIS (Carrion et al., 2013) concerning medieval data related to Southern Italy, also with the implementation of a WebGIS prototype, was developed by Politecnico of Milan research group in the frame of two national projects (PRIN 2006 and PRIN 2009). Usually GIS based on cadastral sources are a little different in structure: in this context not only national, but also regional differences make the comparison of choices and GIS architecture quite awkward. Similar to the Parma condition there are two projects, both about the city of Rome. The first, elaborated by the CROMA group of Roma Tre University and titled “Atlante Storico di Roma Moderna e Contemporanea” (Baiocchi et al., 2005; Lelo et al., 2005), refers to different historical periods of the city: the Map of Nolli of 1748, the PioGregoriano Cadastre Maps over the period 1818 to 1824 and the Census Maps of 1866. The second (Micalizzi et al., 2012; Descriptio Romae, 2015) is developed by DIPSU department of Roma Tre University and brought in 2007 to the realization of a WebGIS of the Gregoriano Cadastre, integrated with other archival documents related to buildings features. For this reason, this informative system goes beyond the traditional use of GIS for urban and territorial analysis, making possible queries about the buildings. In all these projects, open source technologies have been widely used in their realization. For GBHGIS the relational database was, on the first stage, managed with Oracle software, but during the second step of the project, the Vision of Britain system was moved to Postgres and PostGIS, as this opensource software had developed sufficiently to cope with the demands of the system. Both the Southern Italy project and the Gregoriano Cadastre of Rome WebGIS were entirely developed with open-source technologies: in the former the conceptual model of the database was implemented with SQL Power Architect, the database uses PostgreSQL and the WebGIS prototype was developed with QGIS Web Client. The latter instead used Map Server to implement the cartographic engine of the WebGIS, Postgres/PostGIS as Data Base Management System and Apache Web Server and PHP5 to edit and develop the system. This wide use of open source software, even in the management of complex systems such as the British project, testifies to the validity of these products, which are today more and more developed and can achieve performance 191

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

comparable to commercial software but, in many frameworks, with higher flexibility. The paper structure is developed as follows: first, a very brief description of the documents and maps used in the project, as well as the historical context in which they were developed is provided. Then a technical overview on the opensource database architecture of the HGIS system is described. In this context, probably, the project is not particularly innovative with respect to (w.r.t.) other cadastral HGIS. However, the reader should consider that the peculiar nature of historical sources (in particular as far as census and cadastral data are concerned) presents very specific and local features that make every single project innovative in such sense. In addition, being this the first technical contribution about the project, the main section of the paper addresses a new registration technique for the georeferencing stage, while further information about the implementation of the different historical periods and technical details about time-domain management will be provided in future works.

2 The Parma HGIS project The Parma HGIS project is based on the computerization of cadastres and censuses, which, as seen before, are sources of primary importance for the knowledge of the city. Four main historical periods were identified. They correspond to key moments in the history of Parma and to the four main cadastral productions: Sardi Atlas (1767), which summarizes the reformist and illuminated period led by Minister Du Tillot during the first Bourbon government; Bourbon Cadastre (1853) realized during the government of Maria Luigia and considered as a continuation of Napoleon cadastre; Post-Unitarian Cadastre (1901) and Cadastre of 1940. Although the database in general has been structured taking into account all the sources, providing a possible implementation with archival data as deeds, building permits, etc. of all the historic periods, at present, the work was completed entirely only for the Sardi Atlas (with the Bourbon Cadastre at 90% completion). The Sardi Atlas is the first cartographic cadastre of Parma, made between 1765 and 1767 by the cartographer Gian Pietro Sardi. Its realization, promoted by the Minister Guillaume Du Tillot during the first Bourbon government of the city (1749-1804), can refer to the general program of knowledge and urban ornamentation of the city. The Atlas includes maps and registers with details about the particles drawn in the maps (see figure 1.).

192

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

Figure 1 - One of the Sardi Atlas tables. As far as the internal structure is concerned, the Atlas has a table of location in scale 1:5000 that represents the city within the surrounding area and 28 detail tables, approximately in scale 1:850. The image depicted is objective, accurately surveyed and in strictly zenith projection. The tables are wellfinished in the layout, thanks to the frequent presence of drawings on paper edge, and each element, according to the scale of representation, is drawn with the same degree of detail. There is distinction between built and unbuilt areas and particular attention is given to religious buildings, outlining the microplans, which are a section of the ground floor with the drawing of the roofing system. Each of these 28 tables is complementary to another one containing the list of holders of each parcel drawn in the map. The lists are drawn up in tabular form and contain the name of the holder and information on real estate. In this way, thanks to the precise correspondence between maps and lists, each graphic parcel can be associated to its owner. Each parcel is uniquely identified by the combination between its number and the number of block to which it belongs. The maps show, beside the distinction between covered and uncovered areas, also the presence of vegetated areas, place names, the canal system, and therefore are much more detailed than the ones produced by modern cadastre. Lists of owners instead provide information about the possessor, including name and surname, type of institution (if the possessor is not a natural person), title and, sometimes, degrees of relationship, patronymic, right of use of the land, intended use and share ownership of parcel. The connection between graphic tables and registers is through the number of parcel and block.

3 The Database structure From the previous paragraph a complex and varied HGIS structure appeared. This, as far as the data and the relationship are concerned, is due to the coexistence of more historical periods, so distant in time. Approaching the contemporary, in fact, the informative content that can be deduced directly from the cadastral maps becomes more abstract (the maps of Sardi Atlas of 1767, for example, allow highlighting the types of vegetation, the plans of the main buildings, the canal system) but the information in the register associated 193

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

with maps increases. The same consideration can be done w.r.t. censuses, which increasingly characterize in detail the individual inhabitants, allowing their precise placement within the building. Despite of these differences, which can be solved by a progressive increase of the attributes assigned to the same logical-conceptual entity, the type of data contained in the documents remains substantially constant over the time; the data derived from the registers are in fact always cartographic and descriptive, the one deduced from the census are, instead, only descriptive. In other words, we evaluated which was the structure to be used for better overall data management. Among the various possible solutions, the focus has been placed in particular on two alternatives: a structure that would give preference to the internal coherence of the single source, thanks to the creation of specific tables for each, or a structure that, at the expense of the general compactness and consistency on individual sources, would make possible a more homogeneous database of all historical periods. It was decided to adopt this second solution, as it allows more easily the development of diachronic query, maintaining an overall structure rather simple. One of the main system requests, being the HGIS initially devoted to historical study of the city social structure, was to enter data as reported by the source, without any interpretation and with specific archival reference so that the user, most likely an historian, can verify them in any moment. In this way, it is always possible to refer the data to a particular historical framework, with the possibility to separate it from the others. It is also possible to associate with the same object discordant data, gathered from different sources, leaving to the end user the ability to lean towards the greater reliability of one rather than the other. Finally, the precise reference to the source allows the reconstruction of the urban evolutionary process and the transformations occurred. For the choice of the RDBMS (Relational DataBase Management System) to be used for the system, we opted for a platform based on PostegreSQL, with PostGIS extension for spatial data management. The choice was made for several reasons: first of all its open source nature allows to contain costs connected to operation and maintenance of the system, despite sometimes involves more technical complications and cannot always ensure timely technical assistance. Often, to solve some specific issue, a request on one of the many technical forum on the web receive a feedback in few hours, but the users have to faith in the support of the community. While all major GIS software provide very efficient (and easy to use) graphical user interface, with PostGIS spatial database (albeit with different technical complications) it is much easier to expand as much as possible the level of interoperability with different GIS platforms (ArcGIS, AutoCAD Map, QGIS and Grass, etc.). Many of the previous packages (especially commercial ones), while providing enterprise multi-user architectures, require additional modules or complex data administration systems for specific procedure, increasing the final cost. In this context, since one of the main project objective is to provide data to a webGIS platform, to make the system usable by the wider spectrum of users possible, the opportunity not to be bound to a commercial solution provides greater flexibility, guaranteeing also a higher cost limitation. 194

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

The operation of vectorization of the maps was not particularly costly both in terms of time and work organization: the information contained in the maps are, indeed, easily classifiable within the structure of the information system thanks to simple decomposition in graphical units. On the contrary, the insertion of descriptive data contained in the lists of holders was more complex: thematic data are difficult to standardize because their complexity and heterogeneity. A preliminary phase of analysis of the document was therefore necessary to be able to extrapolate the invariant information, on the base of which organize a database structure that allows the inclusion of most of the cases also considering possible exceptions. However, before data insertion into the GIS, a phase of transcription and normalization of all entries in Sardi Atlas lists was carried out. The reason was that the original data were typologically different, written using a wide range of conventions and with a large number of exceptions, anomalies, inconsistencies, which obviously could not be contained in the database tables without negative impact on its functionality. The solution of these problems involved numerous historical researches to avoid oversimplification, distorting the original source. Again, in respect of the source, it was decided to leave traces in the database of the original form of data as reported in the Atlas, but without the insertion of special formatting or graphic signs that are not supported by the system. As can be seen from this brief discussion, the step of transcription of the data has been very demanding in terms of time and difficulties in interpretation. Since they are historical data, their encoding is very complex for both the intrinsic differences and the necessity to keep an attitude of respect of the source. Before inserting the data, is in fact necessary to resolve the issues related to the interpretation of historical fact, sometimes not uniquely interpretable, resulting in a significant lengthening of database implementation. Such peculiarity are, in fact, specific of the Parma cadastres (and huge differences are anyway present between the different historical thresholds) and cannot be inferred or deduced by other HGIS projects.

4 Maps georeferencing One of the main steps that should be carefully considered in developing a Historical GIS is the maps georeferencing stage. The integrated use of coregistered historical and modern maps is probably the first, and for most users the main, requirement for the system itself. At the same time all the different maps, along the centuries, were produced using different surveying and drawing techniques, and were commissioned often with different illustration and documentation purposes: unfortunately map metadata is a modern concept, and is quite rare to have any description about the restitution procedures adopted for the historical maps. Therefore, precision, reliability and correctness of the graphical information should always be examined and evaluated indirectly. Probably, for many HGIS applications, a very accurate maps co-registration is not an essential feature since comparison with other historical periods or with modern cartography is a qualitative operation. The availability of old cadastral maps and historical cartography, are usually considered for analysing land and urban transformations along time. Nonetheless, such analysis commonly does 195

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

not involve a thorough comparison at parcel boundary level, where errors higher than few meters cannot be accepted. Rather, the analysis often considers land and city development at a smaller scale and is focused on macroscopic transformations of areas and land use. Nonetheless, even in those circumstances, where a perfect overlay of the different historical layers is not a severe requirement, it’s important inferring the correctness of the map, highlighting possible discrepancies and making possible to provide at least some hypothesis on the implementation of the map itself: e.g. at the very minimum, the result of the transformation provides information on dimensional parameters of the map and on the scale of original representation, even in cases where they are not known. Often, at the same time, analysing with proper carefulness the residuals of the registration transformation, especially if a comparison/overlap with modern cartography can be done, the accuracy of the map and the mistakes made during the survey and restitution operations can be evaluated. Finally, to critically evaluate the possible discrepancies, the analysis of the map should be considered with respect to its historical and cultural context. Such analysis should consider the scientific and geographical knowledge of the era and the progress of surveying techniques, but also the cultural background and political ideology that influenced greatly cartography in the past, determining types and methods of representation. It would be also very useful to know the author, date of creation, the equipment used, the contents and the objectives of representation, thus being able to provide for any errors (Brovelli et al., 2012). Unfortunately, this information is often missing, and surveying and restitution methodologies remain unknown. Finally uncertainties or lack of information about measurement units, map reference and projection system, as well as interpretation of semantic content, can make the georeferencing process much more difficult and tricky. In the end all these uncertainties, as well as the choice of the registration transform model, affect the final result in terms of discrepancies between the points of the historical and modern map. The residuals, in fact, are the result of a summation of errors inherent to the historical map and errors related to the georeferencing process itself. As far as the historical data are concerned, the total graphical error arises from several causes including survey measures, graphic restitution and the deformations due to the preservation condition of the map. In addition, even if modern instrumentation is usually very accurate, instrumental errors due to the digitalization of the map should be considered. Finally for cadastral historical maps, where high scale factors are usually implemented (e.g. the Sardi Atlas has a 1:850 ca. scale), during co-registration the user should also consider the tolerances of modern surveying equipment or cartographic products used for georeferencing, and consider in addition the possibility that the position of homologous points not necessarily remained unchanged in time. The Sardi Atlas maps were scanned at high resolution (400 dpi) while for acquiring the Ground Control Points (GCP) for map registration the official Topographic Regional Carthography (CTR – nominal scale 1:5000, reference system EPSG 23032) was used. During activity design, we decided to discard the idea of performing a thorough GPS survey of historical points considering not justified the higher cost for GCP materialization compared to the small 196

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

budget for the project and low requests in terms of accuracy. The double points were identified at corners of buildings or blocks of which the position has remained, with all probability, unchanged over time (monuments and historical buildings). While in the central areas of the city their detection did not involve a lot of problems, given the presence of many noble and religious buildings not destroyed during World War II, for many tables in the areas close to city walls the same proved to be more difficult. At the end of the XVIII century, those areas consisted mainly in gardens and cultivated fields and were used just in the next century for city expansion. For this reason while a good number of GCP can be found in the inner part of the city, a proper and reliable co-registration of outer drawings proved to be much harder. For this reason a procedure derived from image block orientation in photogrammetry (and in particular in independent model adjustment) was adapted for the registration stage. Basically, in the same period, a similar approach was independently developed in (Barazzetti et al., 2014) so just few procedure details will be drawn in the following sections. For outer plates, even if few historical GCP are present, many common elements between the maps can be found. For example, on each Atlas table there is a hint to the perimeter of surrounding blocks of neighbouring plates where common points can be easily tracked (in analogy to photogrammetry orientation such points will be defined Tie Point (TP) in the following) and used for mosaicking/registration (see figure 2).

Figure 2 - Image measurements including the different categories of points: TP (white) and GCP (grey). All the registration tools implemented in the most common GIS packages, both commercial (e.g. ESRI ArcMap, ENVI, ERDAS Autosynch, Autodesk Map, etc.) and freeware (e.g. Quantum GIS), have specific feature for map georeferencing. The procedure are usually quite straightforward, since the software allows loading different map sources or point coordinate lists, provides specific tools to allow the operator to identify and extract corresponding points and finally estimate the georeferencing transformation using a specific, user defined, geometric model. In the end the software can produce a World File definition (if 197

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

the model is a translation or an Helmert transformation) and/or resample the original scanned map. Even the simplest software packages have the additional feature, at the end of the procedure, of reporting the results of the transformation, where double points residuals are commonly shown. Nonetheless, as mentioned in (Barazzetti et al., 2014) a strong limitation of many of those software packages is that the procedure is commonly carried out as a progressive registration of maps, since the user can consider just two maps at a time. This means that, especially for those maps where TP are used, the registration errors accumulates along the georeferencing procedure and can make really hard the identification of possible discrepancies, in particular for those maps where no GCP are present and residuals are thus commonly low. For that reason a very simple C# software code was developed: being C# an object-oriented programming language its translation to other platform or languages, e.g. Python or Java, is straightforward. In the proposed methodology all the maps are co-registered concurrently integrating GCP (or image-to-ground points) and TP (or image-to-image points) observations. As far as the transformation model is concerned, every parametric transformation can be taken into account in the processing framework. However, for the project, just two “not exact” (see Brovelli et al., 2012), parametric transformation model were considered: the simplest is a Helmert 2D model where, beside the rotational and translation parameters, the scale factor can be estimated or fixed (using, for instance, the value that can be evaluated using the graphical scale reported on the maps):

(

X =a0 + λ c o s θ ∙ x− λ s i nθ ∙ y= X 0 +a ∙ x−b ∙ y Y =b 0 + λ s i n θ ∙ x+ λ c o s θ ∙ y=Y 0 + a ∙ y +b ∙ x

)

Where X and Y are ground coordinates of object point, X 0 and Y0 are the translation components, λ is the scale factor and θ represents the rotation angle of the transformation. Alternatively, an affine transformation can be used:

(

X =a0 + a1 x+ a2 y Y =b 0 +b 1 x +b 2 y

)

where ai and bi, are free parameters. The transformation model includes, besides a rigid rotation and translation, a non-isotropic scaling, and therefore lengths ratio along different directions and angles are not preserved. Often, in similar cases, an affine transformation is able to correct some deformations that might occur during paper conservation or during the scanning stage (for example due to a not perfect orthogonality or scale coincidence of the scanning axis). However, if just few, not well distributed, double points were selected, the higher transformation degree of freedom can introduce unwanted deformation effects that are difficult to be identified. In this context, a conformal (Helmert) transformation is certainly a more conservative solution. The use of TP has proved essential to apply consistently the transformation to all the tables since, especially for outer areas, in many cases there were less than necessary GCP. Both observation equations (1) or (2) are linear w.r.t. their transformation parameters and can be easily solved (the user might mix both transformation models) with a standard Least Squares Adjustment technique: 198

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015" T

−1

x=  ( A P A )

T

A Pb    

Where A is the design (coefficient) matrix, x the solution (unknown or parameter) vector, b the constant term vector, and P = Cyy-1 is the weight matrix of observation that implements the stochastic model of the solving system. The latter allows specifying different weights, and thus different importance for the final solution, of the different observation. For instance, if the user can quantify, at least approximately, the expected error for GCP equation w.r.t. TP observation, the stochastic model can influence accordingly the final solution consistency. On the other hand, changing the weight of GCP and TP observation, the user might prefer to increase the adherence of the final registration solution with current cartography or, on the contrary, prefer a higher cohesion of adjacent plates, limiting the residual of TPs. In this context, to provide an appropriate (or at least rational) definition of the weights, we considered several components that could affect the final result. First, we considered the factors that affect the correspondence mapping between current and historical maps, as survey errors, definition of the parcel boundary, deformation of the map, poor accuracy in the identification of the points on the CTR (which has a smaller scale compared to the Atlas), etc. The evaluation was empirical and extremely hard to be conducted in quantitative terms, considering the difficulties to clearly determine the various error components. Given the measurement tolerances of modern cartography technology at CTR scale (1:5000), and considered the measuring instruments used for the Sardi Atlas, it was considered for the equations relating to GCP a value of σxy equal to 2 m. On the other hand, considering the precision of the design of Sardi Atlas, and the high coherence between adjacent plates obtained along the perimeter of city blocks, we found that the Atlas presented a very good internal consistency. Given the scale of representation of the Atlas, considered the drawing techniques and the good correspondence of the elements as a result of some tests, for the equations relating to the TP a σ xy = 0.4 m was used. With these values the final global co-registration of the maps provided probably also the most appealing results. The solution shows very good consistency of the elements on the maps border, with little or no troubles in the mosaicking stage (see figure 3a), but still with a good correspondence of historical features with modern buildings (see figure 3b).

199

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

a.

b.

Figure 3 - a. Graphical representation of all the 28 Sardi Atlas tables after mosaicking. b. Overlay of modern CTR with one of the Sardi Atlas table after registration. As far as the transformation model to use is concerned, both Helmert and affine model were considered in our tests. However, from the comparison between the different georeferencing global solutions (we also tried to change the stochastic model to verify if different weights can influence the solution), we found that the results, using the same covariance matrix, were fully comparable and with residual errors very similar. Therefore, considering that the map support showed no particular deformation to justify the application of an affine transformation, it is preferred the use of a conformal transformation model. For outlier rejection, instead of the RANSAC approach proposed in (Barazzetti et al., 2014), expecting few outlier, a much simpler data snooping procedure were implemented.

200

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

6 Conclusion and future development The paper addressed the very early stages of an open-HGIS project regarding the historical cadastral documentation of the city of Parma. At the time of writing the first historical period, represented by the Sardi Atlas of 1767, is completed, and the next historical threshold concerning the Bourbon Cadastre of 1853 is almost done. The next project stages will involve, apart the completion of the Bourbon Cadastre data layers, the insertion of the later cadastral thresholds, and the further addition of other documental sources. From the very beginning of the experimentation, the research pointed out that all the historical documentation are extremely complex in their structure and organization, with numerous ambiguities and intrinsic peculiarities which are difficult to standardize. Historical sources are in fact not homogeneous, both with respect to language and internal organization. Even the historical maps have often problems, especially related to difficult interpretation of descriptive content because of errors or omissions and, in some cases, inaccuracy of drawing or incorrect conservation of the paper support. Therefore, the organization in an encoded form, suitable for computing, of the heterogeneous reality reproduced by the Sardi Atlas was particularly onerous, but necessary for database structuring. At present, it is possible to analyse the city referring to the original map source (see for instance the raster layers of figure 3). In addition, the first “betatesters” of the system can make more complex queries, such as statistical and thematic analysis, related to the holders or to specific features concerning spatial data (see for instance figure 4).

Figure 4 - A thematic view of the Sardi parcel layer where areas are themed differently: built areas (brown), unbuilt areas (beige) and green areas (green). The aim of the project is to make the system usable by the wider spectrum of users possible, also through a webGIS platform. In this regard, issues related to 201

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

the dissemination of the results remain to be investigated, since the historical sources used are property of archives, libraries and museums that often pose restrictions on the disclosure and claim property rights on such sources. Despite these difficulties under solution, in all these contexts of access to data, the choice of implementing the HGIS using open-source geospatial frameworks/software proved to be very successful. With commercial (“closed”) GIS solutions, users are usually more confined in the specific software architecture/workflow, and interoperability between different researches is limited by the software platform itself (often the users must use the same software, with the same modules, to efficiently exchange all the information). On the contrary, an open-source architecture, with software and data infrastructure easily affordable at little or no cost by everyone, is the easier way to ensure that scalability as well as information and expertise exchange can be implemented in a data-driven environment. In this regard, at the end of this first phase of the project, an evaluation of the results can be made: the project involves a significant commitment of resources, since it requires specialized skills and many hours of work by the operators. However, the decision to use an open source platform and to organize the project in different stages delayed in time and executable by more (volunteers?) people, according to a protocol of intent and common behaviour, was taken wittingly to ensure that the project becomes fully realized and with a sustainable financial budget. Furthermore, we believe that the cultural value of the project, linked to the renovated, more efficient access of a documentary heritage of great value not very consulted, but fundamental for historical studies as well as in urban planning activities, is of primary importance for the community.

References ✔ Baiocchi, V., & Lelo, K. (2005, September). Georeferencing the historical maps of Rome between the seventeenth and eighteenth centuries. In CIPA 2005 XX International Symposium-International cooperation to save the world's cultural heritage. Torino (Vol. 26, pp. 114118). ✔ Balletti, C. (2006). Georeference in the analysis of the geometric content of early maps. e-Perimetron, 1(1), 32-42. ✔ Barazzetti, L., Brumana, R., Oreni, D., & Previtali, M. (2014). Historical Map Registration via Independent Model Adjustment with Affine Transformations. In Computational Science and Its Applications–ICCSA 2014 (pp. 44-56). Springer International Publishing. ✔ Brovelli, M. A., & Minghini, M. (2012). Georeferencing old maps: a polynomial-based approach for Como historical cadastres. ePerimetron, 7(3), 97-110. ✔ Carrion D., Migliaccio F., Minini G., Zambrano C., 2013, Rappresentazione cartografica e condivisione di dati storici in ambiente GIS. Atti 17a conferenza nazionale ASITA, 5-7 novembre 2013, Riva del Garda – Italy, pp. 379-384 ✔ Descriptio Romae (2015). http://www.dipsuwebgis.uniroma3.it. Last accessed March, 2nd, 2015. ✔ Gauthiez, B., & Zeller, O. (2009). Espace costruit, espace social à Lyon aux XVII-XIXe seècles: l'apport du SIG. In M. Panzeri, & A. Farruggia, Fonti, metafonti e GIS per l'indagine della struttura storica del territorio (p. 39-49). 202

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

Torino: Celid. ✔ Gauthiez, B., & Zeller, O. (2014). Lyons, the Spatial Analysis of a City in the 17th and 18yh Centuries. Locating and Crossing Data in a GIS Built from Written Sources. Mapping Spatial Relations, Their Perceptions and Dynamics, Lecture Notes in Geoinformation and Cartography, 97-118. ✔ Gregory, I. N., Bennett, C., Gilham, V. L., & Southall, H. R. (2002). The Great Britain Historical GIS Project: from maps to changing human geography. The Cartographic Journal, 39(1), 37-49. ✔ Gregory, I. N., & Ell, P. S. (2007). Historical GIS: technologies, methodologies, and scholarship (Vol. 39). Cambridge University Press. ✔ Knowles, A. K. (2002). Past Time, Past Place: GIS for history A collection of twelve case studies on the use of GIS in historical research and education. ESRI press. ISBN 1-58948-032-5 ✔ Lelo, K., & Travaglini, M. (2005, September). The GIS-based historical atlas of Rome. In XXth International CIPA Symposium (Vol. 26). ✔ Micalizzi, P., Magaudda, S., Buonora, P., & d’Elia, L. S. (2012). A GIS for the city of Rome: archives, architecture, archeology. e-Perimetron, 7(1), 2835.

203

Geomatics Workbooks n° 12 – "FOSS4G Europe Como 2015"

204