2. Writing Guidelines

In general, when creating reST documentation for the QGIS project, please follow the Python documentation style guidelines. For convenience, we provide a set of general rules we rely on for writing QGIS documentation below.

2.1. Writing Documentation

2.1.1. Headlines

To each webpage of the documentation corresponds a .rst file.

Sections used to structure the text are identified through their title which is underlined (and overlined for the first level). Same level titles must use same character for underline adornment. In QGIS Documentation, you should use following styles for chapter, section, subsection and minisec.

********
Chapter
********

Section
=======

Subsection
----------

Minisec
.......

Subminisec
^^^^^^^^^^

2.1.2. Lists

Lists are useful for structuring the text. Here are some simple rules common to all lists:

• Start all list items with a capital letter

• Do not use punctuation after list items that only contain a single simple sentence

• Use period ( . ) as punctuation for list items that consist of several sentences or a single compound sentence

2.1.3. Indentation

Indentation in ReStructuredText should be aligned with the list or markup marker. It is also possible to create block quotes with indentation. See the Specification

#. In a numbered list, there should be
   three spaces when you break lines
#. And next items directly follow

   * Nested lists
   * Are also possible
   * And when they also have
     a line that is too long,
     the text should be naturally
     aligned
   * and be in their own paragraph

However, if there is an unindented paragraph, this will reset the numbering:

#. This item starts at 1 again

2.1.4. Inline Tags

You can use tags to emphasize items.

• Menu GUI: to mark a complete sequence of menu selections, including selecting submenus and choosing a specific operation, or any subsequence of such a sequence.

  :menuselection:`menu --> submenu`
  

• Dialogs and Tab titles: Labels presented as part of an interactive user interface including window titles, tab titles, button and option labels.

  :guilabel:`title`
  

• Filenames and directories

  :file:`README.rst`
  

• Icons with popup text

  |icon| :sup:`popup_text`
  

  (see image below).

• Keyboard shortcuts

  :kbd:`Ctrl+B`
  

  will show Ctrl+B

  When describing keyboard shortcuts, the following conventions should be used:

  • Letter keys are displayed using uppercase: S

  • Special keys are displayed with an uppercase first letter: Esc

  • Key combinations are displayed with a + sign between keys, without spaces: Shift+R

• User text

  ``label``
  

2.1.5. Labels/references

Anchors inside the text can be used to create hyperlinks to sections or pages.

The example below creates the anchor of a section (e.g., Label/reference title)

.. _my_anchor:

Label/reference
---------------

To call the reference in the same page, use

see my_anchor_ for more information.

which will return:

see my_anchor for more information.

Notice that it will jump to the line/thing following the ‘anchor’. You do not need to use apostrophes, but you do need to have empty lines after the anchor.

Another way to jump to the same place from anywhere in the documentation is to use the :ref: role.

see :ref:`my_anchor` for more information.

which will create a link with the caption instead (in this case the title of this section!):

see Labels/references for more information.

So, reference 1 (my_anchor) and reference 2 (Labels/references). Because the reference often displays a full caption, it is not really necessary to use the word section. Note that you can also use a custom caption to describe the reference:

see :ref:`Label and reference <my_anchor>` for more information.

which returns:

see Label and reference for more information.

2.1.6. Figures and Images

Pictures

To insert an image, use

.. figure:: /static/common/logo.png
   :width: 10 em

which returns

Replacement

You can put an image inside text or add an alias to use everywhere. To use an image inside a paragraph, first create an alias in the source/substitutions.txt file:

.. |nice_logo| image:: /static/common/logo.png
               :width: 1 em

and then call it in your paragraph:

My paragraph begins here with a nice logo |nice_logo|.

This is how the example will be displayed:

My paragraph begins here with a nice logo .

To allow preview rendering in GitHub that is as close as possible to HTML rendering, you will also need to add the image replacement call at the end of the file you changed. This can be done by copy-pasting it from substitutions.txt or by executing the scripts/find_set_subst.py script.

Note

Currently, to ensure consistency and help in the use of QGIS icons, a list of aliases is built and available in the Substitutions chapter.

Figure

.. _figure_logo:

.. figure:: /static/common/logo.png
   :width: 20 em
   :align: center

   A caption: A logo I like

The result looks like this:

Fig. 2.20 A caption: A logo I like

To avoid conflicts with other references, always begin figure anchors with _figure_ and use terms that easily connect to the figure caption. While only the centered alignment is mandatory for the image, feel free to use any other options for figures (such as width, height, scale…) if needed.

The scripts will insert an automatically generated number before the caption of the figure in the generated HTML and PDF versions of the documentation.

To use a caption (see My caption) just insert indented text after a blank line in the figure block.

A figure can be referenced using the reference label like this:

see :numref:`figure_logo`

renders like this:

see Fig. 2.20

This is the preferred way of referencing figures.

Note

For :numref: to work, the figure must have a caption.

It is possible to use :ref: instead of :numref: for reference, but this returns the full caption of the image.

see :ref:`figure_logo`

renders like this:

see A caption: A logo I like

Tables

A simple table can be coded like this

=======  =======  =======
x        y        z
=======  =======  =======
1        2        3
4                 5
=======  =======  =======

It will render like this:

x	y	z
1	2	3
4		5

Use a \ (backslash) followed by an empty space to leave an empty space.

You can also make more complicated tables and reference them:

.. _my_drawn_table:

+---------------+--------------------+
| Windows       | macOS              |
+---------------+--------------------+
| |win|         | |osx|              |
+---------------+--------------------+
| and of course not to forget |nix|  |
+------------------------------------+

My drawn table, mind you this is unfortunately not regarded as a caption

You can reference it like this: my_drawn_table_.

The result:

Windows	macOS
and of course not to forget

My drawn table, mind you this is unfortunately not regarded as a caption

You can reference to it like this my_drawn_table.

For even more complex tables, it is easier to use list-table:

.. list-table::
   :header-rows: 1
   :widths: 20 20 20 40

   * - What
     - Purpose
     - Key word
     - Description
   * - **Test**
     - ``Useful test``
     - complexity
     - Geometry.  One of:

       * Point
       * Line

The result:

What	Purpose	Key word	Description
Test	Useful test	complexity	Geometry. One of: Point Line

2.1.7. Index

An index is a handy way to help the reader find information in a document. QGIS documentation provides some essential indices. There are a few rules that help us provide a set of indices that are really useful (coherent, consistent and really connected to each other):

• An index should be human readable, understandable and translatable; an index can be made from many words but you should avoid any unneeded _, -… characters to link them i.e., Loading layers instead of loading_layers or loadingLayers.

• Capitalize only the first letter of the index unless the word has a particular spelling. E.g., Loading layers, Atlas generation, WMS, pgsql2shp.

• Keep an eye on the existing Index list in order to reuse the most convenient expression with the right spelling and avoid unnecessary duplicates.

Several index tags exist in RST. You can use the inline :index: tag within normal text:

QGIS can load several :index:`Vector formats` supported by GDAL/OGR ...

Or you can use the .. index:: block-level markup which links to the beginning of the next paragraph. Because of the rules mentioned above, it is recommended to use the block-level tag:

.. index:: WMS, WFS, Loading layers

It is also recommended to use index parameters such as single, pair and see, in order to build a more structured and interconnected index table. See Index generating for more information on index creation.

2.1.8. Special Comments

Sometimes, you may want to emphasize some points of the description, either to warn, remind or give some hints to the user. In QGIS Documentation, we use reST special directives such as .. warning::, .. seealso::`, ``.. note:: and .. tip::. These directives generate frames that highlight your comments. See Paragraph Level markup for more information. A clear and appropriate title is required for both warnings and tips.

.. tip:: **Always use a meaningful title for tips**

   Begin tips with a title that summarizes what it is about. This helps
   users to quickly overview the message you want to give them, and
   decide on its relevance.

2.1.9. Code Snippets

You may also want to give examples and insert code snippets. In this case, write the comment below a line with the :: directive inserted. For a better rendering, especially to apply color highlighting to code according to its language, use the code-block directive, e.g. .. code-block:: xml. More details at Showing code.

Note

While texts in note, tip and warning frames are translatable, be aware that code block frames do not allow translation. So avoid comments not related to the code and keep comments as short as possible.

2.1.10. Footnotes

Please note: Footnotes are not recognized by any translation software and it is also not converted to pdf format properly. So, if possible, don’t use footnotes within any documentation.

This is for creating a footnote (showing as example 1)

blabla [1]_

Which will point to:

1

Updates of core plugins

2.2. Managing Screenshots

2.2.1. Add new Screenshots

Here are some hints to create new, nice looking screenshots. The images should be placed in an image (img/) folder that is located in the same folder as the referencing .rst file.

• You can find some prepared QGIS-projects that are used to create screenshots in the ./qgis-projects folder of this repository. This makes it easier to reproduce screenshots for the next version of QGIS. These projects use the QGIS Sample Data (aka Alaska Dataset), which should be placed in the same folder as the QGIS-Documentation Repository.

• Reduce the window to the minimal space needed to show the feature (taking the whole screen for a small modal window > overkill)

• The less clutter, the better (no need to activate all the toolbars)

• Don’t resize them in an image editor; the size will be set into the .rst files if necessary (downscaling the dimensions without properly upping the resolution > ugly)

• Cut the background

• Make the top corners transparent if the background is not white

• Set print size resolution to 135 dpi (e.g. in Gimp set the print resolution Image ► Print size and save). This way, images will be at original size in html and at a good print resolution in the PDF. You can also use ImageMagick convert command to do a batch of images:

  convert -units PixelsPerInch input.png -density 135 output.png
  

• Save them as .png (to avoid .jpeg artifacts)

• The screenshot should show the content according to what is described in the text

Tip

If you are on Ubuntu, you can use the following command to remove the global menu function and create smaller application screens with menus:

sudo apt autoremove appmenu-gtk appmenu-gtk3 appmenu-qt

2.2.2. Translated Screenshots

Here are some additional hints for those that want to create screenshots for a translated user guide:

Translated images should be placed in a img/<your_language>/ folder. Use the same filename as the english ‘original’ screenshot.

2.3. Documenting Processing algorithms

If you want to write documentation for Processing algorithms, consider these guidelines:

• Processing algorithm help files are part of QGIS User Guide, so use the same formatting as User Guide and other documentation.

• Each algorithm documentation should be placed in the corresponding provider folder and group file, e.g. the algorithm Voronoi polygon belongs to the QGIS provider and to the group vectorgeometry. So the correct file to add the description is: source/docs/user_manual/processing_algs/qgis/vectorgeometry.rst.

  Note

  Before starting to write the guide, check if the algorithm is already described. In this case, you can enhance the existing description.

• It is extremely important that each algorithm has an anchor that corresponds to the provider name + the unique name of the algorithm itself. This allows the Help button to open the Help page of the correct section. The anchor should be placed above the title, e.g. (see also the Labels/references section):

  .. _qgisvoronoipolygons:
  
  Voronoi polygons
  ----------------
  

  To find out the algorithm name you can just hover the mouse on the algorithm in the Processing toolbox.

• Avoid using “This algorithm does this and that…” as the first sentence in the algorithm description. Try to use more general expressions like:

  Takes a point layer and generates a polygon layer containing the...
  

• Avoid describing what the algorithm does by replicating its name and please don’t replicate the name of the parameter in the description of the parameter itself. For example if the algorithm is Voronoi polygon consider to describe the Input layer as Layer to calculate the polygon from.

• Indicate in the description whether the algorithm has a default shortcut in QGIS or supports in-place editing.

• Add images! A picture is worth a thousand words! Use .png format and follow the general guidelines for documentation (see the Figures and Images section for more info). Put the image file in the correct folder, i.e. the img folder next to the .rst file you are editing.

• If necessary, add links in the “See also” section that provide additional information about the algorithm (e.g., publications or web-pages). Only add the “See also” section if there is really something to see. As a good practice, the “See also” section can be filled with links to similar algorithms.

• Give clear explanation for algorithm parameters and outputs: take inspiration from existing algorithms.

• Avoid duplicating detailed description of algorithm options. Add this information in the parameter description.

• Avoid adding information about the vector geometry type in the algorithm or parameter description, as this information is already available in the parameter descriptions.

• Add the default value of the parameter, e.g.:

  * - **Number of points**
    - ``NUMBER_OF_POINTS``
    - [number]
  
      Default: 1
    - Number of points to create
  

• Describe the type of input supported the parameters. There are several types available you can pick one from:

  Parameter/Output type	Description	Visual indicator
  Point vector layer	vector: point
  Line vector layer	vector: line
  Polygon vector layer	vector: polygon
  Generic vector layer	vector: any
  Vector field numeric	tablefield: numeric
  Vector field string	tablefield: string
  Vector field generic	tablefield: any
  Raster layer	raster
  Raster band	raster band
  HTML file	html
  Table layer	table
  Expression	expression
  Point geometry	coordinates
  Extent	extent
  CRS	crs
  Enumeration	enumeration
  List	list
  Number	number
  String	string
  Boolean	boolean
  Folder path	folder
  File	file
  Matrix	matrix
  Layer	layer
  Same output type as input type	same as input
  Definition	definition
  Point	point
  MultipleLayers	multipleLayers
  Range	range
  AuthConfig	authconfig
  Mesh	mesh
  Layout	layout
  LayoutItem	layoutitem
  Color	color
  Scale	scale

• Study an existing and well documented algorithm, and copy all the useful layouts.

• When you are finished, just follow the guidelines described in A Step By Step Contribution to commit your changes and make a Pull Request

Here is an example of an existing algorithm to help you with the layout and the description:

.. _qgiscountpointsinpolygon:

Count points in polygon
-----------------------
Takes a point and a polygon layer and counts the number of points from the
point layer in each of the polygons of the polygon layer.
A new polygon layer is generated, with the exact same content as the input
polygon layer, but containing an additional field with the points count
corresponding to each polygon.

.. figure:: img/count_points_polygon.png
  :align: center

  The labels in the polygons show the point count

An optional weight field can be used to assign weights to each point.
Alternatively, a unique class field can be specified. If both options
are used, the weight field will take precedence and the unique class field
will be ignored.

``Default menu``: :menuselection:`Vector --> Analysis Tools`

Parameters
..........

.. list-table::
   :header-rows: 1
   :widths: 20 20 20 40

   * - Label
     - Name
     - Type
     - Description
   * - **Polygons**
     - ``POLYGONS``
     - [vector: polygon]
     - Polygon layer whose features are associated with the count of
       points they contain
   * - **Points**
     - ``POINTS``
     - [vector: point]
     - Point layer with features to count
   * - **Weight field**

       Optional
     - ``WEIGHT``
     - [tablefield: numeric]
     - A field from the point layer.
       The count generated will be the sum of the weight field of the
       points contained by the polygon.
   * - **Class field**

       Optional
     - ``CLASSFIELD``
     - [tablefield: any]
     - Points are classified based on the selected attribute and if
       several points with the same attribute value are within the
       polygon, only one of them is counted.
       The final count of the points in a polygon is, therefore, the
       count of different classes that are found in it.
   * - **Count field name**
     - ``FIELD``
     - [string]

       Default: 'NUMPOINTS'
     - The name of the field to store the count of points
   * - **Count**
     - ``OUTPUT``
     - [vector: polygon]

       Default: [Create temporary layer]
     - Specification of the output layer type (temporary, file,
       GeoPackage or PostGIS table).
       Encoding can also be specified.

Outputs
.......

.. list-table::
   :header-rows: 1
   :widths: 20 20 20 40

   * - Label
     - Name
     - Type
     - Description
   * - **Count**
     - ``OUTPUT``
     - [vector: polygon]
     - Resulting layer with the attribute table containing the
       new column with the points count