Ouverture des données¶

Charger une couche à partir d’un fichier¶

To load a layer from a file, you can:

• for vector data (like Shapefile, Mapinfo or dxf layer), click on ^{Add Vector Layer} toolbar button, select the Layer ‣ Add Layer ‣ Add Vector Layer menu option or press Ctrl+Shift+V. This will bring up a new window (see figure_vector_add) from which you can check File and click on [Browse]. You can also specify the encoding for the file if desired.

  

  Fenêtre d’ajout d’une couche vectorielle

• for raster layers, click on the ^{Add Raster Layer} icon, select the Layer ‣ Add Layer ‣ Add Raster Layer menu option or type Ctrl+Shift+R.

That will bring up a standard open file dialog (see figure_vector_open), which allows you to navigate the file system and load a shapefile, a geotiff or other supported data source. The selection box Filter allows you to preselect some supported file formats. Only the formats that have been well tested appear in the list. Other untested formats can be loaded by selecting All files (*.*).

Fenêtre d’ouverture de données vectorielles dont le format est géré par OGR

Selecting a file from the list and clicking [Open] loads it into QGIS. More than one layer can be loaded at the same time by holding down the Ctrl or Shift key and clicking on multiple items in the dialog. Figure_vector_loaded shows QGIS after loading the alaska.shp file.

QGIS après avoir chargé le Shapefile de l’Alaska

Using the ^{Add Vector Layer} tool:

• You can also load specific formats like ArcInfo Binary Coverage, UK. National Transfer Format, as well as the raw TIGER format of the US Census Bureau or OpenfileGDB. To do that, you’d need to select Directory as Source type. In this case a directory can be selected in the dialog after pressing [Browse].

• With the Database source type you can select an existing database connection or create one to the selected database type. Available database types are ODBC, OGDI Vectors, Esri Personal Geodatabase, MySQL as well as PostgreSQL or MSSQL.

  Pressing the [New] button opens the Create a New OGR Database Connection dialog whose parameters are among the ones you can find in Créer une connexion enregistrée. Pressing [Open] you can select from the available tables for example of the PostGIS enabled database.

• The last source type, Protocol, enables to open data from the web using for example GeoJSON or CouchDB format. After selecting the type you have to fill URI of the source.

Importing a delimited text file¶

Delimited text file (e.g. .csv, .txt) can be loaded in QGIS using the tools described above. However, loaded this way, it’ll show up like a simple table data. Sometimes, delimited text files can contain geometric data you’d want to visualize; this is what the Add Delimited Text Layer is designed for.

Click the toolbar icon ^{Add Delimited Text Layer} in the Manage layers toolbar to open the Create a Layer from a Delimited Text File dialog, as shown in figure_delimited_text.

Fenêtre d’ajout de couche depuis un fichier texte délimité

First, select the file to import (e.g., qgis_sample_data/csv/elevp.csv) by clicking on the [Browse] button. Once the file is selected, QGIS attempts to parse the file with the most recently used delimiter. To enable QGIS to properly parse the file, it is important to select the correct delimiter. You can specify a delimiter by activating:

• CSV (comma separated values);
• Custom delimiters, choosing among some predefined delimiters like comma, space, tab, semicolon...;
• or Regular expression delimiter and entering text into the Expression field. For example, to change the delimiter to tab, use \t (this is a regular expression for the tab character).

Once the file is parsed, set Geometry definition to Point coordinates and choose the X and Y fields from the dropdown lists. If the coordinates are defined as degrees/minutes/seconds, activate the DMS coordinates checkbox.

Finally, enter a layer name (e.g., elevp), as shown in figure_delimited_text. To add the layer to the map, click [OK]. The delimited text file now behaves as any other map layer in QGIS.

There is also a helper option that allows you to trim leading and trailing spaces from fields — Trim fields. Also, it is possible to Discard empty fields. If necessary, you can force a comma to be the decimal separator by activating Decimal separator is comma.

If spatial information is represented by WKT, activate the Well Known Text option and select the field with the WKT definition for point, line or polygon objects. If the file contains non-spatial data, activate No geometry (attribute only table) and it will be loaded as an ordinal table.

En complément, vous pouvez activer :

• Use spatial index to improve the performance of displaying and spatially selecting features;
• Use subset index;
• Watch file to watch for changes to the file by other applications while QGIS is running.

Importing a DXF or DWG file¶

DXF and DWG files can be added to QGIS by simple drag-and-drop from the common Browser Panel. You’ll be prompted to select the sublayers you’d like to add to the project. Layers are added with random style properties.

To keep the dxf/dwg structure and its symbology in QGIS, you may want to use the dedicated Project ‣ DWG/DXF Import... tool. Indeed, the DWG/DXF Import dialog allows you to import into GeoPackage database any element of the drawing file.

In the dialog, you have to:

• Input a location for a GeoPackage file, that will be created to store the DWG/DXF content to;
• Specify which coordinate system the data in the DWG data is in;
• Then use the [Import] button to select the DWG/DXF file to use (one per geopackage). The GeoPackage database will be automatically populated with the drawing file content. Depending on the size of the *CAD file, this could take some time;
• The Expand block references will transform the existing blocks into normal elements;
• the Use curves promotes the output layers geometry type to a curved one.

After the .dwg or .dxf data is imported into the GeoPackage database the frame in the lower half of the dialog is populated with the list of layers from the imported file. There you can select which layers to add to the QGIS project:

• At the top, set a Group name to group the drawing files in the project;
• Check layers to show: Each selected layer is added to an ad hoc group which contains vector layers for the point, line, label and area features of the drawing layer. The style of each layer is setup so that it resembles the look it originally had in *CAD;
• Check whether layer should be visible at opening;
• Alternatively using the Merge layers option places all layers in a single group;
• Press [OK] to open the layers in QGIS.

Importer des données vecteur OpenStreetMap¶

Ces dernières années, le projet OpenStreetMap (OSM) a gagné en popularité, car dans beaucoup de pays, aucune donnée géographique sous licence libre, telle que par exemple le réseau routier, n’est disponible. L’objectif du projet OSM est de créer une base de données géographiques libre sur le monde entier et qui est éditable par tous à partir de données GPS, de photographies aériennes ou tout simplement des connaissances locales du terrain. Pour soutenir ce projet, QGIS fournit une extension qui permet aux utilisateurs de travailler avec les données OSM.

Using the Browser Panel, you can load a .osm file to the map canvas, in which case you’ll get a dialog to select sublayers based on the geometry type. The loaded layers will contain all the data of that geometry type in the file and keep the osm file data structure.

To avoid working with a such complex data structure, and be able to select only features you need based on their tags, QGIS provides a core and fully integrated OpenStreetMap import tool:

• To connect to the OSM server and download data, open the menu Vector ‣ OpenStreetMap ‣ Download data.... You can skip this step if you already obtained an .osm XML file using JOSM, Overpass API or any other source;
• The menu Vector ‣ OpenStreetMap ‣ Import Topology from XML... will convert your .osm file into a SpatiaLite database and create a corresponding database connection;
• The menu Vector ‣ OpenStreetMap ‣ Export Topology to SpatiaLite... then allows you to open the database connection, select the type of data you want (points, lines, or polygons) and choose tags to import. This creates a SpatiaLite geometry layer that you can add to your project by clicking on the ^{Add SpatiaLite Layer} toolbar button or by selecting the Add SpatiaLite Layer... option from the Layer menu (see section Couches SpatiaLite).

GPS¶

Loading GPS data in QGIS can be done using the core plugin: GPS Tools. Instructions are described in Section Extension GPS.

GRASS¶

Le travail sur des couches vectorielles GRASS est décrit dans la Section Intégration du SIG GRASS.

Couches SpatiaLite¶

The first time you load data from a SpatiaLite database, begin by:

• clicking on the ^{Add SpatiaLite Layer} toolbar button;
• selecting the Add SpatiaLite Layer... option from the Layer ‣ Add Layer menu;
• or by typing Ctrl+Shift+L.

This will bring up a window that will allow you either to connect to a SpatiaLite database already known to QGIS, which you can choose from the drop-down menu, or to define a new connection to a new database. To define a new connection, click on [New] and use the file browser to point to your SpatiaLite database, which is a file with a .sqlite extension.

QGIS gère les vues SpatiaLite éditables.

Database related tools¶

Créer une connexion enregistrée¶

In order to read and write tables from the many database formats QGIS supports you’ll need to create a connection to that database. While QGIS Browser Panel is the simplest and recommanded way to connect and use databases within, QGIS provides specific tools you can use to connect to each of them and load their tables:

• Add PostGIS Layer... or by typing Ctrl+Shift+D
• Add MSSQL Spatial Layer or by typing Ctrl+Shift+M
• Add Oracle Spatial Layer... or typing Ctrl+Shift+O
• Add DB2 Spatial Layer... or typing Ctrl+Shift+2

These tools are accessible either from the Manage Layers Toolbar or the Layer ‣ Add Layer ‣ menu. Connecting to SpatiaLite database is described at Couches SpatiaLite.

Astuce

Create connection to database from the QGIS Browser Panel

Select the corresponding database format in the Browser tree, right-click and choose connect will provide you with the database connection dialog.

Most of the connection dialogs follow a common basis that will be described below using the PostGreSQL database tool as example.

The first time you use a PostGIS data source, you must create a connection to a database that contains the data. Begin by clicking the appropriate button as exposed above, opening an Add PostGIS Table(s) dialog (see figure_add_postgis_tables). To access the connection manager, click on the [New] button to display the Create a New PostGIS Connection dialog.

Create a New PostGIS Connection Dialog

The parameters required for a PostGIS connection are exposed below. For the other database types, see their differences at Particular Connection requirements.

• Nom : Un nom pour cette connexion. Il peut être identique à Base de données.

• Service : Paramètre de nom de service à utiliser alternativement au couple hôte/port (et potentiellement base de données). Il peut être défini dans pg_service.conf. Consultez la section PostgreSQL Service connection file pour plus de détails.

• Hôte : Nom pour l’hôte de la base de données. Il doit s’agir d’un nom existant, car il sera utilisé pour ouvrir une connexion TCP/IP ou interroger l’hôte. Si la base de données est sur le même ordinateur que QGIS, mettez simplement localhost.

• Port : numéro de port que le serveur de base de données PostgreSQL écoute. Le port par défaut est 5432.

• Base de données : nom de la base de données.

• Mode SSL : Comment sera négociée la connexion SSL avec le serveur. Notez qu’une importante accélération du rendu des couches PostGIS peut être obtenue en désactivant le SSL dans l’éditeur de connexion. Les options suivantes sont proposées :

  • Désactive : Essaye uniquement une connexion SSL non cryptée.

  • Permet : Essaye une connexion non-SSL. En cas d’échec, essaye une connexion SSL.

  • Préfère (par défaut) : Essaye une connexion SSL. En cas d’échec, essaye une connexion non-SSL.

  • *Requiertù : Essaye uniquement une connexion SSL.

• Nom d’utilisateur : Nom d’utilisateur utilisé pour se connecter à la base de données.

• Mot de passe : mot de passe associé au Nom d’utilisateur pour se connecter à la base de données.

  You can save any or both of the username and password parameters, in which case they will be used by default each time you need to connect to this database. If not saved, you’ll be prompted to fill the missing credentials to connect to the database in next QGIS sessions; meanwhile the connection parameters you entered are stored in a temporary internal cache and returned whenever a username/password for the same database is requested, until you close the current QGIS process.

  Warning

  Paramètres utilisateur de QGIS et Sécurité

  In the Authentication tab, saving username and password will keep unprotected credentials in the connection configuration. Those credentials will be visible if, for instance, you shared the project file with someone. Therefore, it’s advisable to save your credentials in a Authentication configuration instead (Configurations tab - See Système d’authentification for more details) or in a service connection file (see PostgreSQL Service connection file for example).

Optionally, depending on the type of database, you can activate the following checkboxes:

• N’afficher que les couches dont la géométrie est listée (dans geometry_columns)

• Ne pas résoudre le type pour les géométries non restreintes (GEOMETRY)

• Ne regarder que dans le schéma ‘public’

• Lister les tables sans géométrie

• Utiliser la table des métadonnées estimées

Astuce

Utiliser la table de métadonnées estimées pour accélérer les opérations

Lorsque les couches sont initialisées, plusieurs requêtes doivent être lancées pour établir les caractéristiques des géométries contenus dans la table de la base de données. Lorsque l’option Utiliser la table de métadonnées estimées est cochée, ces requêtes examinent uniquement un nombre restreint de lignes et utilisent la table des statistiques plutôt que la totalité de la table. Cela peut accélérer drastiquement les performances sur des données volumineuses mais peut entraîner une caractérisation incorrecte (ex: le décompte des entités des couches filtrées ne sera pas déterminé avec précision) ainsi qu’un comportement anormal lorsque des colonnes qui devraient être uniques ne le sont pas.

Once all parameters and options are set, you can test the connection by clicking on the [Test connection] button or apply it hitting [OK]. From the Add PostGIS Table(s), click now on [Connect] and the dialog is filled with tables from the selected database (as shown in figure_add_postgis_tables).

[water_service]
host=192.168.0.45
port=5433
dbname=gisdb
user=paul
password=paulspass

[wastewater_service]
host=dbserver.com
dbname=water
user=waterpass

Loading a Database Layer¶

Once you have one or more connections defined to a database (see section Créer une connexion enregistrée), you can load layers from it. Of course, this requires having available data. See e.g. section Importer des données dans PostgreSQL for a discussion on importing data into a PostGIS database.

To load a layer from a database, you can perform the following steps:

1. Open the “Add <database> table(s)” dialog (see Créer une connexion enregistrée),
2. Choose the connection from the drop-down list and click [Connect].

3. Cochez ou décochez selon votre besoin Lister les tables sans géométrie

4. Optionally, use some Search Options to reduce the list of tables to those matching your search. You can also set this option before you hit the [Connect] button, speeding this way the database fetching.

5. Trouvez la ou les couches que vous souhaitez ajouter dans la liste des couches disponibles.

6. Select it by clicking on it. You can select multiple layers by holding down the Shift key while clicking.
7. If applicable, use the [Set Filter] button (or double-click the layer) to start the Query builder dialog (See section Constructeur de requête) and define which features to load from the selected layer. The filter expression appears in the sql column. This restriction can be removed or edited in the Layer Properties ‣ General ‣ Provider Feature Filter frame.
8. The checkbox in the Select at id column that is activated by default gets the features ids without the attributes and speed in most cases the data loading.
9. Click on the [Add] button to add the layer to the map.

Add PostGIS Table(s) Dialog

Astuce

Load database table(s) from the Browser Panel

Like simple files, connected database are also listed in the Browser Panel. Hence, you can load tables from databases using the Browser:

1. Find the layer to use with the ^{Filter Browser} tool at the top the browser panel (see The Browser Panel for the search options);
2. select and drag-and-drop it in the map canvas.