4. Features

View data
Explore data and compose maps
Create, edit, manage and export data
Analyze data
Publish maps on the Internet
Extend QGIS functionality through plugins
- Core Plugins
- External Python Plugins
Python Console
Known Issues
- Number of open files limitation

QGIS offers a wealth of GIS functions, provided by core features and plugins. The locator bar makes it easy to search for functions, datasets and more.

A short summary of six general categories of features and plugins is presented below, followed by first insights into the integrated Python console.

4.1. View data 

You can view combinations of vector and raster data (in 2D or 3D) in different formats and projections without conversion to an internal or common format. Supported formats include:

Spatially-enabled tables and views using PostGIS, SpatiaLite and MS SQL Spatial, Oracle Spatial, vector formats supported by the installed OGR library, including GeoPackage, ESRI Shapefile, MapInfo, SDTS, GML and many more. See section Working with Vector Data.
Raster and imagery formats supported by the installed GDAL (Geospatial Data Abstraction Library) library, such as GeoTIFF, ERDAS IMG, ArcInfo ASCII GRID, JPEG, PNG and many more. See section Working with Raster Data.
Mesh data (TINs and regular grids are supported). See Working with Mesh Data.
Vector tiles
GRASS raster and vector data from GRASS databases (location/mapset). See section GRASS GIS Integration.
Online spatial data served as OGC Web Services, including WMS, WMTS, WCS, WFS, and WFS-T. See section Working with OGC / ISO protocols.

The QGIS authentication infrastructure helps you manage user/password, certificates and keys for web services and other resources.
Spreadsheets (ODS / XLSX)

Temporal data are supported.

4.2. Explore data and compose maps 

You can compose maps and interactively explore spatial data with a friendly GUI. The many helpful tools available in the GUI include:

QGIS browser
On-the-fly reprojection
2D and 3D map rendering
DB Manager
Print layout
Report
Overview panel
Spatial bookmarks
Annotation tools
Identify/select features
Edit/view/search attributes
Data-defined feature labeling
Data-defined vector and raster symbology tools
Atlas map composition with graticule layers
North arrow, scale bar and copyright label for maps
Support for saving and restoring projects

4.3. Create, edit, manage and export data 

You can create, edit, manage and export vector and raster layers in several formats. QGIS offers the following:

Vector digitizing tools
Ability to create and edit multiple file formats and GRASS vector layers
Georeferencer plugin to geocode images
GPS tools to import and export GPX format, and convert other GPS formats to GPX or down/upload directly to a GPS unit (on Linux, usb: has been added to list of GPS devices)
Support for visualizing and editing OpenStreetMap data
Ability to create spatial database tables from files with the DB Manager plugin
Improved handling of spatial database tables
Tools for managing vector attribute tables
Option to save screenshots as georeferenced images
DXF-Export tool with enhanced capabilities to export styles and plugins to perform CAD-like functions

You can perform spatial data analysis on spatial databases and other OGR-supported formats. QGIS currently offers vector analysis, raster analysis, sampling, geoprocessing, geometry and database management tools. You can also use the integrated GRASS tools, which include the complete GRASS functionality of more than 400 modules (see section GRASS GIS Integration). Or, you can work with the Processing plugin, which provides a powerful geospatial analysis framework to call native and third-party algorithms from QGIS, such as GDAL, SAGA, GRASS, OTB, R, and more (see section Introduction). All analysis functions are run in the background, allowing you to continue your work before the processing has finished.

The graphical modeller allows you to combine / chain functions into a complete workflow in an intuitive graphical environment.

4.5. Publish maps on the Internet 

QGIS can be used as a WMS, WMTS, WMS-C, WFS, OAPIF and WFS-T client (see section Working with OGC / ISO protocols), and QGIS Server (see QGIS Server Guide/Manual) allows you to publish your data through the WMS, WCS, WFS and OAPIF protocols on the Internet using a webserver.

4.6. Extend QGIS functionality through plugins 

QGIS can be adapted to your special needs with the extensible plugin architecture and libraries that can be used to create plugins. You can even create new applications with C++ or Python!

4.6.1. Core Plugins 

Core plugins include:

DB Manager (exchange, edit and view layers and tables from/to databases; execute SQL queries)
Geometry Checker (check geometries for errors)
Georeferencer GDAL (add projection information to rasters using GDAL)
GPS Tools (load and import GPS data)
GRASS (integrate GRASS GIS)
MetaSearch Catalogue Client (interacting with metadata catalog services supporting the OGC Catalog Service for the Web (CSW) standard)
Offline Editing (allow offline editing and synchronizing with databases)
Processing (the spatial data processing framework for QGIS)
Topology Checker (find topological errors in vector layers)

4.6.2. External Python Plugins 

QGIS offers a growing number of external Python plugins that are provided by the community. These plugins reside in the official Plugins Repository and can be easily installed using the Python Plugin Installer. See Section The Plugins Dialog.

4.7. Python Console 

For scripting, it is possible to take advantage of an integrated Python console, which can be opened with: Plugins ► Python Console. The console opens as a non-modal utility window. For interaction with the QGIS environment, there is the qgis.utils.iface variable, which is an instance of QgisInterface. This interface provides access to the map canvas, menus, toolbars and other parts of the QGIS application. You can create a script, then drag and drop it into the QGIS window and it will be executed automatically.

For further information about working with the Python console and programming QGIS plugins and applications, please refer to QGIS Python console and PyQGIS Developer Cookbook.

4.8. Known Issues 

4.8.1. Number of open files limitation 

If you are opening a large QGIS project and you are sure that all layers are valid, but some layers are flagged as bad, you are probably faced with this issue. Linux (and other OSs, likewise) has a limit of opened files by process. Resource limits are per-process and inherited. The ulimit command, which is a shell built-in, changes the limits only for the current shell process; the new limit will be inherited by any child processes.

You can see all current ulimit info by typing:

$ ulimit -aS

You can see the current allowed number of opened files per process with the following command on a console:

$ ulimit -Sn

To change the limits for an existing session, you may be able to use something like:

$ ulimit -Sn #number_of_allowed_open_files
$ ulimit -Sn
$ qgis

To fix it forever

On most Linux systems, resource limits are set on login by the pam_limits module according to the settings contained in /etc/security/limits.conf or /etc/security/limits.d/*.conf. You should be able to edit those files if you have root privilege (also via sudo), but you will need to log in again before any changes take effect.

More info:

https://www.cyberciti.biz/faq/linux-increase-the-maximum-number-of-open-files/ https://linuxaria.com/article/open-files-in-linux