Deschiderea datelor¶

Încărcarea unui strat dintr-un fișier¶

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.

  

  Add Vector Layer Dialog

• 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 (*.*).

Open an OGR Supported Vector Layer Dialog

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 with Shapefile of Alaska loaded

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 Creating a stored Connection. 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.

Delimited Text Dialog

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.

Additionally, you can enable:

• 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.

Importarea Vectorilor OpenStreetMap¶

In recent years, the OpenStreetMap project has gained popularity because in many countries no free geodata such as digital road maps are available. The objective of the OSM project is to create a free editable map of the world from GPS data, aerial photography or local knowledge. To support this objective, QGIS provides support for OSM data.

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 Straturile SpatiaLite).

GPS¶

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

GRASS¶

Working with GRASS vector data is described in Section Integrarea GRASS GIS.

Straturile 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 also supports editable views in SpatiaLite.

Database related tools¶

Creating a stored Connection¶

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 Straturile SpatiaLite.

Tip

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.

• Name: A name for this connection. It can be the same as Database.

• Service: Service parameter to be used alternatively to hostname/port (and potentially database). This can be defined in pg_service.conf. Check the PostgreSQL Service connection file section for more details.

• Host: Name of the database host. This must be a resolvable host name such as would be used to open a TCP/IP connection or ping the host. If the database is on the same computer as QGIS, simply enter localhost here.

• Port: Port number the PostgreSQL database server listens on. The default port for PostGIS is 5432.

• Database: Numele bazei de date.

• SSL mode: How the SSL connection will be negotiated with the server. Note that massive speed-ups in PostGIS layer rendering can be achieved by disabling SSL in the connection editor. The following options are available:

  • Disable: Only try an unencrypted SSL connection;
  • Allow: Try a non-SSL connection. If that fails, try an SSL connection;
  • Prefer (the default): Try an SSL connection. If that fails, try a non-SSL connection;
  • Require: Only try an SSL connection.

• Username: User name used to log in to the database.

• Password: Password used with Username to connect to the database.

  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

  QGIS User Settings and Security

  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 Sistem de Autentificare 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:

• Only show layers in the layer registries
• Don’t resolve type of unrestricted columns (GEOMETRY)
• Only look in the ‘public’ schema
• Also list tables with no geometry
• Use estimated table metadata

Tip

Use estimated table metadata to speed up operations

When initializing layers, various queries may be needed to establish the characteristics of the geometries stored in the database table. When the Use estimated table metadata option is checked, these queries examine only a sample of the rows and use the table statistics, rather than the entire table. This can drastically speed up operations on large datasets, but may result in incorrect characterization of layers (eg. the feature count of filtered layers will not be accurately determined) and may even cause strange behaviour in case columns that are supposed to be unique actually are not.

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

Încărcarea unui Strat al unei Baze de date¶

Once you have one or more connections defined to a database (see section Creating a stored Connection), you can load layers from it. Of course, this requires having available data. See e.g. section Importing Data into 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 Creating a stored Connection),
2. Choose the connection from the drop-down list and click [Connect].
3. Select or unselect Also list tables with no geometry.
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. Find the layer(s) you wish to add in the list of available layers.
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 Constructorul de Interogări) 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

Tip

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 Panoul Navigatorului for the search options);
2. select and drag-and-drop it in the map canvas.