22.3. Creating an Output — QGIS Documentation documentation (2024)

22.3.1. Export settings

Whenever you export a print layout, there are a selection of export settings QGIS needsto check in order to produce the most appropriate output. These configurationsare:

• The Export settings of the Layoutpanel, such as Export resolution, Print as rasterAlways export as vectors or Save world file

• Exclude page from exports in the page item properties panel

• Exclude item from exports in the item properties panel

Moreover, a number of predefined checks are automatically applied to the layout.Currently these checks include testing that scalebars are correctly linked to map items,and that map overview items are also correctly linked to a map.If the checks fail, you are shown a nice warning advising you of the issue.

22.3.2. Export as Image

To export a layout as an image:

1. Click the ^{Export as image} icon

2. Select the image format, the folder and filename (e.g. myill.png)to use.If the layout contains more than one page, each page will be exported toa file with the given filename with the page number appended(e.g. myill_2.png).

3. In the next (Image Export Options) dialog:

   • You can override the print layout Export resolution and theexported page dimensions (as set in Layout panel).

   • Image rendering can also be improved with the Enableantialiasing option.

   • If you want to export your layout as a georeferenced image (e.g., toshare with other projects), check the Generateworld file option, and an ESRI World File with the same name as theexported image, but a different extension (.tfw for TIFF,.pnw for PNG, jgw for JPEG, …) will be created whenexporting.This option can also be checked by default in the layout panel.

     Note

     For multi-page output, only the page that contains thereference map will get a world file (assuming that theGenerate world file option is checked).

   • By checking Crop to content option, the image outputby the layout will include the minimal area enclosing all the items (map,legend, scale bar, shapes, label, image…) of each page of the composition:

     • If the composition includes a single page, then the output is resized toinclude EVERYTHING on the composition. The page can then be reduced orextended to all items depending on their position (on, above, below, left orright of the page).

     • In case of a multi-page layout, each page will be resized to include items inits area (left and right sides for all pages, plus top for the first page andbottom for the last page). Each resized page is exported to a separate file.

     The Crop to content dialog also lets you add margins aroundthe cropped bounds.

   • By checking Open file after exporting the exportedfile will automatically open in the default image viewer.

22.3.3. Export as SVG

To export a layout as SVG:

1. Click the ^{Export as SVG} icon

2. Fill in the path and filename (used as a base name for all thefiles in case of multi-page composition, as for image export)

3. In the next SVG Export Options dialog, you can override thelayout default export settings or configurenew ones:

   • Export map layers as SVG groups: exported items aregrouped within layers whose name matches the layer names from QGIS, makingit much easier to understand the contents of the document.

   • Always export as vectors: some rendering optionsrequire items to be rasterized for a better rendering. Check this option tokeep the objects as vectors with the risk that the appearance of the outputfile may not match the print layout preview (for more details, seeExport settings).

   • Export RDF metadata of the document such as thetitle, author, date, description…

   • Simplify geometries to reduce output file size: thisavoids exporting ALL geometry vertices, which can result in a ridiculouslycomplex and large export file size that could fail to load in other applications.Geometries will be simplified while exporting the layout in order to removeany redundant vertices which are not discernably different at the exportresolution (e.g. if the export resolution is 300 dpi, vertices that areless than 1/600 inch apart will be removed).

   • Set the Text export: controls whether text labels are exportedas proper text objects (Always export texts as textobjects) or as paths only (Always export texts as paths).If they are exported as text objects, they can be edited in externalapplications (e.g. Inkscape) as normal text. BUT the side effect is thatthe rendering quality is reduced, AND there are issues with rendering whencertain text settings like buffers are in place. That’s why exporting aspaths is recommended.

   • Apply Crop to content option

   • Disable tiled raster layer exports: When exportingfiles, QGIS uses a built-in raster layer tiled rendering that saves memory.Sometimes, this can cause visible “seams” in the rastersfor generated files. Checking this option would fix that, at the cost of ahigher memory usage during exports.

   • By checking Open file after exporting the exportedfile will automatically open in the default SVG viewer.

22.3.4. Export as PDF

To export a layout as PDF:

1. Click the ^{Export as PDF} icon

2. Fill in the path and filename: unlike for image and SVG export, all thepages in the layout are exported to a single PDF file.

3. In the next PDF Export Options dialog, you can override thelayout default export settings or configurenew ones:

   • Always export as vectors: some rendering optionsrequire items to be rasterized for a better rendering. Check this option tokeep the objects as vectors with the risk that the appearance of the outputfile may not match the print layout preview (for more details, seeExport settings).

   • Append georeference information: available only ifthe reference map, from which the information is taken,is on the first page.

   • Export RDF metadata of the document such as thetitle, author, date, description…

   • Set the Text export: controls whether text labels are exportedas proper text objects (Always export texts as textobjects) or as paths only (Always export texts as paths).If they are exported as text objects then they can be edited in externalapplications (e.g. Inkscape) as normal text. BUT the side effect is thatthe rendering quality is decreased, AND there are issues with rendering whencertain text settings like buffers are in place. That’s why exporting aspaths is recommended.

   • Control the PDF Image compression using:

     • Lossy (JPEG), which is the default compression mode

     • or Lossless, which creates bigger files in most cases, but ismuch more suitable for printing outputs or for post-production in externalapplications (requires Qt 5.13 or later).

   • Create Geospatial PDF (GeoPDF):Generate a georeferenced PDF file.

   • Disable tiled raster layer exports: When exportingfiles, QGIS uses tiled based rendering that saves memory.Sometimes, this can cause visible “seams” in the rasters for generated files.Checking this option would fix that, at the cost of a higher memory usageduring exports.

   • Simplify geometries to reduce output file size:Geometries will be simplified while exporting the layout by removingvertices that are not discernably different at the export resolution(e.g. if the export resolution is 300 dpi, vertices that are lessthan 1/600 inch apart will be removed).This can reduce the size and complexity of the export file (very largefiles can fail to load in other applications).

   • By checking Open file after exporting the exportedfile will automatically open in the default PDF viewer.

22.3.5. Generate an Atlas

Atlas functions allow you to create map books in an automated way.Atlas uses the features of a table or vector layer(Coverage layer) to create an output for each feature(atlas feature) in the table / layer.The most common usage is to zoom a map item to the current atlasfeature.Further use cases include:

• a map item showing, for another layer, only features that share the sameattribute as the atlas feature or are within its geometry.

• a label or HTML item whose text is replaced as features are iterated over

• a table item showing attributes of associated parent or children features of the current atlas feature…

For each feature, the output is processed for all pages and items accordingto their exports settings.

To enable the generation of an atlas and access atlas parameters, refer tothe Atlas panel. This panel contains the following(see Fig. 22.66):

• Generate an atlas enables or disables atlasgeneration.

• Configuration

  • A Coverage layer combo box that allows you tochoose the table or vector layer containing the features to iterate over.

  • An optional Hidden coverage layer that, if checked,will hide the coverage layer (but not the other layers) during the generation.

  • An optional Page name combo box to specify the name for thefeature page(s).You can select a field of the coverage layer or set anexpression.If this option is empty, QGIS will use an internal ID, according to thefilter and/or the sort order applied to the layer.

  • An optional Filter with text area that allows youto specify anexpression for filtering features from the coverage layer. If the expressionis not empty, only features that evaluate to True will be processed.

  • An optional Sort by that allows you tosort features of the coverage layer (and the output), using a field of thecoverage layer or an expression.The sort order (either ascending or descending) is set by the two-stateSort direction button that displays an up or a down arrow.

• Output - this is where the output of the atlas can be configured:

  • An Output filename expression textbox that is used to generatea filename for each atlas feature. It is based on expressions.is meaningful only for rendering to multiple files.

  • A Single file export when possible that allows you toforce the generation of a single file if this is possible with the chosen outputformat (PDF, for instance). If this field is checked, the value of theOutput filename expression field is meaningless.

  • An Image export format drop-down list to select the output formatwhen using the ^{Export atlas as Images…} button.

The area of [% concat( upper(CITY_NAME), ',', ZIPCODE, ' is ',format_number($area/1000000, 2) ) %] km2

The area of [% upper(CITY_NAME)%],[%ZIPCODE%] is[%format_number($area/1000000,2) %] km2

The area of PARIS,75001 is 1.94 km2

22.3.5.3. Explore Data-defined override buttons with atlas

There are several places where you can use a ^{Data defined override} button to override the selected setting.This is particularly useful with atlas generation.See Data defined override setup for more details on this widget.

For the following examples the Regions layer of the QGIS sampledataset is used and selected as Coverage layer forthe atlas generation.We assume that it is a single page layout containing a map item anda label item.

When the height (north-south) of a region extent is greater than itswidth (east-west), you should use Portrait instead of Landscapeorientation to optimize the use of paper.With a ^{Data Defined Override} button you candynamically set the paper orientation.

Right-click on the page and select Page Properties to open thepanel. We want to set the orientation dynamically, using an expressiondepending on the region geometry, so press the button offield Orientation, select Edit… to open theExpression string builder dialog and enter the followingexpression:

CASE WHEN bounds_width(@atlas_geometry) > bounds_height(@atlas_geometry)THEN 'Landscape' ELSE 'Portrait' END

Now if you preview the atlas, the paper orients itselfautomatically, but item placements may not be ideal. For each Region you need toreposition the location of the layout items as well. For the map item you canuse the button of its Width property to set itdynamic using the following expression:

@layout_pagewidth - 20

Likewise, use the button of the Height property toprovide the following expression to constrain map item size:

@layout_pageheight - 20

To ensure the map item is centered in the page, set its Referencepoint to the upper left radio button and enter 10 for its Xand Y positions.

Let’s add a title above the map in the center of the page. Select the labelitem and set the horizontal alignment to Center.Next move the label to the right position, choose the middle button forthe Reference point, and provide the following expression forfield X:

@layout_pagewidth / 2

For all other layout items you can set the position in a similar way so theyare correctly positioned both for portrait and landscape.You can also do more tweaks such as customizing the title withfeature attributes (see Customize labels with expression example), changing images,resizing the number of legend columns number according to page orientation,…

The information provided here is an update of the excellent blog (in Englishand Portuguese) on the Data Defined Override optionsMultiple_format_map_series_using_QGIS_2.6 .

Another example for using data-defined override buttons is the usage of a dynamicpicture. For the following examples we use a geopackage layer containing a BLOB fieldcalled logo with the field type binary (see Creating a new GeoPackage layer).For every feature there is defined a different picture so that the atlas can iterateover as described in Preview and generate an atlas.All you need to do is add a picture in the print layout and go to itsItem properties in the atlas context. There you can find adata-defined override button in the Image source section of theMain Properties.

In the following window choose Edit so that the Expression String Builderopens. From the Fields and values section you can find the BLOB field thatwas defined in the geopackage layer. Double-click the field name logo and click OK.

The atlas iterates over the entries in the BLOB field provided that you choose the geopackagelayer as Coverage layer (further instructions you can find in Preview and generate an atlas).

These are just two examples of how you can use some advanced settings with atlas.

22.3.5.4. Preview and generate an atlas

Once the atlas settings have been configured, and layout items (map, table,image…) linked to it, you can create a preview of all the pages by choosingAtlas ► Preview Atlas or clicking the ^{Preview Atlas} icon.You can then use the arrows to navigate through all the features:

• ^{First feature}

• ^{Previous feature}

• ^{Next feature}

• ^{Last feature}

You can also use the combo box to select and preview a specific feature.The combo box shows atlas feature names according to the expression set in theatlas Page name option.

As for simple compositions, an atlas can be generated in different ways (seeCreating an Output for more information -just use tools from the Atlas menu or toolbar instead of theLayout menu.

This means that you can directly print your compositions withAtlas ► Print Atlas.You can also create a PDF using Atlas ► Export Atlas as PDF…:You will be asked for a directory to save all the generated PDF files,except if the Single file export when possible has beenselected. In that case, you’ll be prompted to give a filename.

With Atlas ► Export Atlas as Images… orAtlas ► Export Atlas as SVG… tool, you’re also prompted toselect a folder. Each page of each atlas feature composition is exported tothe image file format set in Atlas panel or to SVG.

Note

With multi-page output, an atlas behaves like a layout in that only thepage that contains the General settings will get a world file (foreach feature output).

Tip

Print a specific atlas feature

If you want to print or export the composition of only one feature of the atlas,simply start the preview, select the desired feature in the drop-down listand click on Layout ► Print (or Export…to any supported file format).

// Declare the two HTML div elements we will use for the parent feature id// and information about the children<div id="parent"></div><div id="my_children"></div><script type="text/javascript"> function setFeature(feature) { // Show the parent feature's identifier (using its "ID" field) document.getElementById('parent').innerHTML = feature.properties.ID; //clear the existing relation contents document.getElementById('my_children').innerHTML = ''; feature.properties.my_relation.forEach(function(child_feature) { // for each related child feature, create a list element // with the feature's name (using its "NAME" field) var node = document.createElement("li"); node.appendChild(document.createTextNode(child_feature.NAME)); document.getElementById('my_children').appendChild(node); }); }</script>