Tag Archives: interpolation

Piracy and corsairs in the Mediterranean Sea

Objectives and deliverables

The aim of this project is to build a GIS layer that shows the level of “piracy-danger” in the Mediterranean Sea. In order to reach this goal, we will proceed step-by-step. The first important step is to choose the period of interest for all the project (included in the Middle Age). After that, a first map will be established with all the maritime routes used formerly by the venetian cargoes for trades and exchanges between harbours. Indeed, these transportations of goods interested a lot the pirates. A second map can be produced with the area usually visited by pirates based on old stories found in literature and potentially in logbooks or diaries. During the last step, these two maps will be used in order to form a final raster map showing the Mediterranean areas with the corresponding level of threat for each pixel using an interpolation model. This will be the final deliverable. Further details for each steps are presented in the following.


1) First map: the principal maritime routes.

The first task is to find the reliable information that will permit to construct this map. The idea is to find literature about the types of goods that were transported by the cargoes in the Mediterranean Sea, at the period of interest. This could be found by consulting old harbour’s archives that compile all relevant information about the route of each specific ship, i.e. the harbour of departure, the one of arrival and possible intermediate harbours. These information are probably archived in harbour’s registers, especially in the Venetian haven’s archives. The other crucial point is the location of the principal harbours of the Mediterranean Sea, at this period. Thanks to these preliminary researches, we will be able to understand roughly the distribution of the principal maritimes routes and which goods are transported in the area of interest. To compile all these information, it would be useful to create a basic database, using, for example mySQL tools to create a complete table. This table will contain the following attributes, based on the results of the research part:

Harbour of departure Harbour of arrival List of intermediate harbours Goods transported

We will fill in this table step-by-step depending on the information that we can found in the literature. Obviously, the main issue will be to define when to finish the filling… and it will depend on the number of reliable information that we could find. After the creation of this table, we have to pass from a simple database to spatial domain. In order to be able to represent the principal maritime routes, we have to use a GIS-software, say Quantum GIS. First of all, we have to located precisely the principal harbours by points, with geographical coordinates, on a vectorial layer. This will be the base to draw the line of maritime routes, using tools of Quantum GIS like joins, spatial joins and generation of spatial flux using tools like MMQGIS. This work will result in a vectorial layer showing a lot of lines representing all the routes (it’s also possible to aggregate these lines to bigger lines regarding the number of ships that navigate these waters). Possibly, we could color these lines depending on the type of good transported. Thanks to that, we could be able to understand where are the likely areas of piracy, using QGIS tools as density calculations based on the number of lines. Indeed, areas, where there is a lot of ships that transport “valuable” goods, are potentially more likely visited by the pirates than areas without maritime traffic.

Example of possible maritime flux layer [2].
 2) Second map: from the piracy stories to the map.

 Stories about piracy and corsairs in Mediterranean Sea are data we can find. Thus, one part of this step is to find these information in different medium such as historical books, logbooks, and old maps. For all the sources of information found, we will extract the place/localisation associated with the story. The occurrence of these localisations will be counted and stored in a table. Here, we can notice a potential issue we may meet regarding the reliability of these data. Indeed, some mentioned locations may not explicitly exist or their names could have changed and thus, it makes their geolocalizations on a map much more difficult. Then, the last part is to map (in the same GIS-software) these locations visited by pirates. The idea is to represent each location with a circle proportional to the number of citations in the different studied stories. This map will give an overview of the more likely places in the Mediterranean Sea where pirates and corsairs were, based only on stories found in literature. The following step will use this representation in addition with the maritime routes map to produce the final map.

3) Final map: piracy and corsairs in Mediterranean Sea.

 This first step will be done by “human-based analysis”. In fact, we will superpose the two first layers in order to have all the information on a same common medium to compare easily their intrinsic information. The goal is to detect the Mediterranean zones where: there is a high probability, mid-probability and really low probability to meet pirates. This analysis will be done according to these two layers and our knowledges about the goods that the pirates prefer, based on the literature researches about the pirates. Based on the detection of these zones, we can construct a new vectorial layer, which will contain only points of probable zones of presence of the pirates. These points will receive a label that will be inserted in a new attribute of their associated table: 100 if it’s absolutely probable to meet pirates, 50 if we think it’s possible but not sure and 0 for zones where there is no risk (because there is no routes or no interesting goods for the pirates), for example. Then, we would like to provide even more precise information by using interpolation to produce raster map. Indeed, in this case, the geostatistics must be the appropriate tool for this purpose. First, the spatial distribution of the piracy in Mediterranean has to be extracted from the last built map by using a so-called variogram, which is a statistical tool to deduce the distribution of the data and the influences between them. Basically, it can inform how a specific location visited by pirates will influence another close or far location in term of apparition of pirates. Finally, we can, for example, use the Kriging method to interpolate the data, based on the spatial distribution carefully found before. This final step gives a smooth distribution of danger with respect to piracy over the whole Mediterranean sea with the error associated with the interpolation. To perform the interpolation, tools like those that are available in the GIS-software SAGA GIS or in R could be useful.

Example of interpolated map [3].

Project plan

 The following timeline in a rough distribution of the differents tasks over the semester.



[1] Featured image: http://www.crystalinks.com

[2] http://sig2010.esrifrance.fr/

[3] http://spatial-analyst.net/wiki/index.php?title=Spatial_interpolation_exercises_(NL)