Paris Metropolitan, an evolution

Definition of the project

The group first selected a range of different maps showing the Paris Metropolitan at different years. In total, we collected from Gallica a set of two maps of the planning of the metro, from the definition of the routes to the addition of stations, a first map from 1908 of the actual metro after its construction in 1990, a second map from 1915, with already visible impacts of the first war, and a third map from 1950, a more contemporain look at the metro as we know it today. Our first idea was to analyse these maps in order to understand the evolution of the Paris Metropolitan, how different areas of major cultural attractions evolved around or hand in hand with the metro stations and how it was impacted by catastrophic events such as wars. However, as the goal of the project is to produce a working interface within a short amount of time, we decided to reduce the work of extraction of data to one map, which is the first map from 1908. Based on this map, we thus intend to build a superposition of a current map from Paris and the metro network extracted from the old map. From this visual display, will be able to see the evolution of the Paris Metropolitan from 1908 until nowadays and important historical explanations will be linked to corresponding stations. The result should take the form of a website page that displays the interactive map. The users would have the possibility to display the different layers, namely the layer of the old map, its metro network, with stations and lines, and this on top of a current map of Paris. Popup windows on each stations would display specific historical information about the station, which would be linked to the sources.
It is based on this prototype that the possibility to conduct similar data extractions on the other maps selected will be considered.

Main steps

• Download in high resolution the different maps
• Create a list of all stations from the first map of 1908
• Determine the main cultural attractions around these stations
• Georeferencing the map from 1908
• Create maps alignment with a contemporain map of Paris
• Extract paths and stations from the map
• Determine or extract coordinates of the different stations
• Create a Database with all the information gathered for each station from 1908
• Compare the first path and stations from 1908 with the actual built one
• Create a website in order to display the maps in an interactive way
  • pop up windows on specific points, such as stations with strong historical backgrounds
  • an overlay of maps in order to better see the evolution from 1908 to nowadays

Milestones

Week 9 (14.11 - 16.11):

• Georeference, alignment with contemporain map and extraction of the paths and stations
• Preparation of the structure of a GeoJSON database
• Preparation of the midterm presentation
• Finalisation of milestones

Week 10 (21.11 - 23.11):

• Analyse of the evolution of the Paris Metropolitan based on the information gathered
• Finish Database in GeoJSON
• Finish writing the description of the extraction methods
• Planning for the creation of a website

Week 11 (28.11 - 30.11):

• Creation of the website to display the data
• Implementation of an interactive map

Week 12 (5.12 - 7.12):

• Finalization of the project
• Finish writing the report (historical introduction to the map, analysis of the performance of extraction, motivation and description of the services)

Detailed description of the extraction methods

In order to extract information from the map, we decided to work with the open source software QGIS3.
This software is a powerful GIS platform which enables to georeference maps, draw points, lines and polygones in order to create new and interactive maps or to enhance and analyse existing ones. It benefits from a good community of users, with even a specific associative platform for Switzerland.
The extraction of the information from the Paris map of 1908 required different steps, from the georeferencing to the extraction of the metropolitan network itself.

Georeferencing

The first step of the work with the 1908 map consists of georeferencing it, namely register it with a coordinate system in order to map it with a location on the surface of the earth . Indeed, the basic map of the Metropolitan of Paris is just an image file that does not contain any geographic information such as coordinates. In order to create these coordinates, we had to work with a shapefile of the buildings of the city of Paris. These ressources are easily found "online", as their are freely made available by the city of Paris . This shapefile is first imported in the new project created in QGIS. Then, the CRS (Coordonate Reference System) we are working with in the context of the project has to be correctly set to the french CRS, called RGF93. After having synchronized the layers with this CRS, the plugin Géoréférenceur GDAL is used. It consists of a window, from which our image, the Paris map of 1908, is imported as a raster and displayed. A raster is an image file to which is added georeferencing information . In order to determine the right coordinates on the image of 1908, a tool from the plugin enables to find matching points from the image to the shapefile of the city of Paris. The work consists of selecting a point on the image and to then find its visual correspondance on the shapefile of the buildings of Paris. We chose these points according to recognizable buildings which exists on both maps. In the end, a total of 6 coordinate points in order to launch the georeferencing. The transformation we then performed was generated with a Polynomiale 1 and a .tiff file was created. This .tiff file contains both the image and the coordinate information of the raster and can be used as a foundation for the following steps of the project.

Overlaying the old map on a contemporain basemap

Now that we have our old map as a raster, its image can be easily placed on top of a contemporain map with the help of its coordinates. QGIS3 proposes a feature called XYZ Tiles and which enables to easily add a corresponding basemap from the "openstreetmap website".

Extracting information

Based on the raster created, the extraction of information can be performed. In order to extract the different stations, a Shapefile has to be created. A Shapefile, already introduced previously for the georeferencing, is a set of different files, .shp, .dbf, .shx, .prj, which all contains information that enables to create a map, with a coordinate system and a visual display via points, vectors or polygons. When creating a new layer Shapefile with QGIS, the name has to specified as well as the type of geometry aforesaid that can either be points, lines or polygons. Then, a list of fields can be define. This list of field is later filled for each point created and can constitute a database.

Railway stations

For the layer containing information about the stations, the type of geometry used is the point. We also added two fields of information. A first string field called Name, in order to store the name of the station, and a second string field called Ligne, in order to store the name of the line the station belongs to. Then, each station visible on the old Metropolitan map from Paris was selected with a point and given a Name and a Ligne accordingly.

Railway lines

We then created a second layer of Shapefile for the lines of the metro. The geometry used for this purpose is the line and the string field Name was created. In order to map the vectors of the line with the exact coordinate of the stations previously set and create a coherent path, the snapping feature of QGIS3 was enabled. The snapping enables to select a perimeter of anchor of a point on a layer. When drawing a line, existing points are then working as magnets and attract the line in order to make it pass through it. Thus, the 6 different lines of the Metropolitan of Paris from 1908, namely line 1, 2 Nord and 2 Sud, 3, 4, 5, 6, where created and passing through the exact coordinates of the stations previously established.

Selected maps

The different maps selected for the project are the following:

• 

  Plan de Paris, avec le tracé du chemin de fer métropolitain (projet de l'administration) et les différentes lignes d'omnibus et de tramways, 1882

• 

  Plan de Paris [indiquant les lignes projetées du chemin de fer métropolitain en souterrain, tranchée, Viaduc, 1895

• 

  Paris, chemin de fer métropolitain ; lignes en exploitation, 1908

• 

  Paris Nouveau plan de Paris avec toutes les lignes du Métropolitain et du Nord-Sud, 1915

• 

  Paris. Plan d'ensemble par arrondissements. Métropolitain : vers 1950