Author: Dr. Miguel Ángel Latre-Abadía
Member of the Advanced Information Systems Laboratory (IAAA)
Why does a major avenue in a city runs the way it does? Why is a square located exactly where it is? The Spanish philosopher, parliamentarian, politician and diplomat Juan Donoso Cortés stated once that “In the past rests the history of the future". It may turn out that the great avenue lays where the medieval walls of the city stood, and the square where one of its doors was located.
We are result of our own history, and this can be clearly seen in the way human settlements in general (and cities in particular) evolve over time. The historical archives of different public administrations have the originals, or reproductions, of the shape and perceived vision of our cities many years ago, represented in maps. In some cases, these resources have been preserved and safeguarded for many years and have served as a basis for very different, interesting and needed research works. It is not until a few years ago when the interest of its use and dissemination through the general citizens has been generated. In this line, the web is the most appropriate means of popularization these days. However, in order perform this dissemination, there are three major challenges to be addressed:
Scanning documents in high resolution. The state of historical cartography in its original media (paper), like in the case of any other type of physical document, degrades over time, even with optimal storage and handling conditions when used. A solution to contribute to its preservation is the digitization of this material. This way, besides the original document (of course still to be preserved), there are digital copies that can be consulted without any type of restrictions caused by the need of preservation of the original. These copies must be carefully done, with much respect and precaution to the original media. In many cases, specific infrastructures are needed (like large tables, high resolution cameras, tripods, illumination sets, etc.) and high resolution and detail is required so that the digital copy can replace the original document for as many queries as possible.
Map georeferencing. The portrait and orientation presented in historical maps is sometimes strange to us because it is outside the patterns we are used to: the North upside, the South downwards and the origin of coordinates in the Equator and the Greenwich meridian. As an example, even nowadays, many maps of Seville have the North pointing to the left and maps of Barcelona can be slightly rotated to accommodate the perfectly orthogonal streets of the Exiample with the vertical and horizontal axis of the map. It is also worth remembering that until 1884 the pattern regarding Greenwich meridian was not adopted. For a long time, the prime meridian was the Ferro Meridian, in the Spanish island of El Hierro, the most western point of the known Europe (thus, negative coordinates were avoided). So, the assignment of current coordinates to singular points of historical maps leads in many cases to rotations and distortions in the map that must be treated with great care by the software helping in these operations. This georeferencing makes possible the use of techniques and tools belonging to the Geographic Information Systems field, and allows for the homogeneous comparison among the different historical maps with each other and with the current cartography.
Cartography publishing. The volume and size that the digitized and georeferenced maps may have once fully processed makes inviable its mere publication in web pages for downloading: very high bandwidth should be required to provide the user a positive experience. In addition, the possibilities of interaction with the downloaded map would depend on the software available to the user, and could be limited, in the worst case scenario, to the plain visualization of the map as an image. Publishing through OGC standard services such as WMS and WMTS, solves the bandwidth problem, because the user no longer needs the full resolution digital resource. The way these services work implies that only images of a size in pixels equivalent to the resolution of the user screen are going to be requested, not depending at all on the map scale. However, these services are intended for software developers and not for end users. Thinking in the later, an application (ideally a web application) must be provided, allowing them to access the maps without any problems of bandwidth and, in addition, providing them functionality to browse the historical maps in a comfortable and effective way. For example: by selecting the year of the historical map you want to see, clicking, searching for current streets or comparing with the current map by selecting different levels of transparency.
The Advanced Information Systems Lab, in collaboration with GeoSLab, the Office of Participation, Transparency and Open Government of the City Council of Zaragoza and the Municipal Archive, and within the European project ENERGIC OD, has worked in the line of digitally publishing historical plans based on Spatial Data Infrastructures. The result is reflected in a new web application, “Zaragoza histórica”, integrated the portal of the Spatial Data Infrastructure of the City of Zaragoza.
This new service was officially launched last March and provides Zaragoza citizens and tourists with a visualisation tool that combines current cartography with a selection of historical maps from Municipal Archive of Zaragoza.
This new service disposes of an interactive viewer that makes possible to overlay a selection of the historic maps catalogue of Zaragoza on the actual cartography and compare the evolution of the city.
So far, there has been published a collection composed by 20 maps of XVIII, XIX, XX y XXI centuries that will be enriched in the future. A careful work of digitalization and georeferencing of maps, together with the availability of a mature map visualization technology, have made possible the development of this interesting tool for analysing the evolution of the city.