Posted in January 2014

QGIS – Two neat features in 2.2

Here’s a quick run-down on two nice new styling options which I’ve recently added to QGIS 2.2.

Map styling for compositions

This little feature was suggested by Mathieu Pellerin, who is always pushing the boundaries of QGIS’ cartographic tools and coming up with great ideas for new styling features (you can check out some of his work via Flickr). Mathieu’s idea was for a new ‘$map‘ variable for the expression builder. This variable holds the id of the map item which is drawing the map, and allows for some nice tweaking of maps in the composer.

The $map variable is most useful when you have more than one map in your composition. The example below shows $map being used to change the styling of a single layer from the main map to the smaller inset map:

Using $map to style two maps with different colours

Using $map to style a single layer in two maps with different colours

In this example the composition has two maps, the larger has an id of “main_map” and the smaller has “inset_map“. The boundary layer has been styled using the rule based renderer, with one rule for $map=’main_map’ and one for $map=’inset_map’, as shown below:

Rule based rendering using the $map variable

Rule based rendering using the $map variable

The end result is that the layer will be rendered using the two different styles depending on which composer map item it is being drawn into. This trick can also be used to tweak labelling rules between the maps. In the example above I’ve restricted the labelling to only show in the main map. This is achieved by setting an expression for the data defined “Show label” property. I’ve used the expression “$map=’main_map’” so that labels are only shown in the main map and not the smaller inset map.

Tweaking label settings using the $map variable

Tweaking label settings using the $map variable

This small addition to QGIS 2.2 allows for some rather powerful improvements to multi-map compositions!

Drawing polygon borders only inside the polygon

The second new feature I wanted to highlight is a new option for polygon outlines which causes the outline to be drawn only on the inside of a polygon feature. The usual behaviour is for outlines to be drawn directly over the centre of the feature boundary, so that half of the outline is drawn inside the feature and half on the outside.

Simple Line Fill before

This means that the outline in a simple line symbol layer overlaps into the neighbouring polygons, and the result is that outlines from these features blend together:

Shaded borders pre QGIS 2.2

Shaded borders pre QGIS 2.2 – see how the colours bleed into the neighbouring features and overlap

This looks like a big muddy mess. A feature I’ve wanted for a long time is the ability to restrict these outlines so that they are only drawn inside the feature. This effect is commonly seen in world atlases and National Geographic maps, where each neighbouring country is shaded with it’s own unique outline colour. Now it’s possible to do this in QGIS just by ticking a single box!

The new "Draw line only inside polygon" option

The new “Draw line only inside polygon” option

As you can see in the above image, the simple line outline style has a new checkbox, “Draw line only inside polygon“. Ticking this box will clip the outline so that only the portion of it which falls inside the feature is rendered. Here’s the result:

Shaded borders with "Draw line only inside polygon" checked

Shaded borders with “Draw line only inside polygon” checked

So much nicer then the earlier output – now none of the borders overlap into their neighbouring regions! Ok, so it is possible to achieve a similar result by creating a specially crafted layer consisting of negatively buffered polygons subtracted from the original polygons, but this takes a lot of fiddling around. It also has the major disadvantage in that the result is scale dependant, and zooming in or out of the map will alter the size of the polygon outlines. But using this wonderful new checkbox in QGIS, we get proper scale-independent borders, and zooming in or out of the map keeps a consistent border width!

Zooming in keeps a consistent border width...

Zooming in keeps a consistent border width…

So there we go – two small new features added in QGIS 2.2 which have huge potential for your cartographic outputs! As per usual, if you come up with some fancy way of utilising these, don’t forget to add your maps to the QGIS Showcase on Flickr.

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Waiting for QGIS 2.2 – Composer Improvements (part 3)

Following on from parts 1 and 2, here’s some more composer changes which are coming in QGIS 2.2

  • Rotation support for all composer item types. Now anything you draw in a composer can be rotated, including scale bars, legends, attribute tables and html frames! Rotation of text labels has also been improved by making the border and background of labels respect the rotation of the label.
Every composer item can now be rotated...

Every composer item can now be rotated…

  • Resizing of rotated items has been improved. Now it’s possible to easily resize rotated items while keeping their correct shape. (There’s still one missing ingredient for complete support here – shear/perspective transforms. Unfortunately this will probably have to wait till 2.4).
Better resizing of rotated items

Better resizing of rotated items

  • Rulers can be shown or hidden in compositions
  • The ruler appearance has been tweaked, adding smaller divisions and better text placement
The ruler appearance has been tweaked

New tweaked appearance for rulers

  • A zoom to actual size button and short cut (Ctrl + 1) have been added
Zoom to 100%

New Zom to 100% button

  • Lastly, the status bar has a new zoom combo box, which shows the current zoom level and allows for quick zoom to several predefined levels. You can also enter an exact zoom level in the box for precise control.
New zoom levels combo box in the status bar

New zoom levels combo box in the status bar

As you can see, the print composer in QGIS 2.2 just keeps getting better! There’s a few other really exciting new additions which have landed recently too, but they deserve their own blog posts. Stay tuned…

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Waiting for QGIS 2.2 – Gradient Fills

One of the big features I worked on for QGIS 2.2 is gradient fill symbols for polygons. In my view QGIS’ symbol support is one of its biggest strengths — the versatility of its symbol layers coupled with the powerful data defined properties support allows for so many effects which just aren’t possible in other GIS packages. Gradient fill support is a nice addition to these features and should help make QGIS even more attractive to cartographers. In this post I’m going to give a quick run through of how gradient fills work in QGIS, and some of the options available for tweaking them.

Gradient fills are enabled through the Style tab in the properties for a vector layer. The default fill for a polygon in QGIS is “Simple fill”, so to switch a layer to a gradient fill you first need to select the “Simple fill” layer, then change the “Symbol layer type” dropdown  to “Gradient fill”:

Gradient Fill type

As you can see, there’s a lot of options in QGIS which can be tweaked for gradient fills. I’ll run through each of them now and explain a little bit about how each one can be used.

Colour modes

QGIS supports two different types of colour modes for gradient fills. The first is a simple “Two color” gradient, where the colour smoothly blends from the first colour to the second. The second mode, “Color ramp” allows you to use any of the standard or user-defined QGIS colour ramps, which can consist of multiple colour stops:

Colour options in gradient fills

Colour options in gradient fills

So, when would you use these options? Well, any time you need more than two colours or need to tweak the position of any of the colours in the gradient you’ll have to use a colour ramp.  If instead you’re just wanting a quick-and-easy gradient then the two colour option might be more suitable.

One last important distinction is that the colours in a two colour gradient can be set using a data defined expression:

Data defined gradient colours

Data defined gradient colours. Please try to use them more tastefully then this!

Gradient types

The next option for gradient fills is rather self-explanatory: gradient types. QGIS supports linear, radial and conical gradients:

Gradient types

Coordinate modes

The coordinate mode option is a little trickier to explain. The default setting, “Object“, will cause the gradient to be drawn entirely within each separate feature. You can see in the example below that every lake feature is coloured with a gradient which starts with light blue in the top left and darkens to a deeper blue in the bottom right. This gradient fill is repeated for all the lake features:

Gradient object coordinate mode

The “Object” coordinate mode for gradient fills

In contrast, the “Viewport” coordinate mode causes the gradient to be drawn across the entire current view of the map. So only the lakes in the top left of the map are drawn with the light blue colour, and the lakes in the bottom right with the deeper blue:

Gradient "viewport" coordinate mode

The “Viewport” coordinate mode for gradient fills

The choice of coordinate mode will depend entirely on your cartographic desires for your map!

Reference points

QGIS gradient fills allow the setting of two “reference points“. These points control where the gradient fill begins and ends. It’s easiest to visualise how these work by imagining a square defined by the points (0, 0) in the top left and (1, 1) in the bottom right. The two reference points fall somewhere within this square. So, the default reference points of (0.5, 0) and (0.5, 1.0) represent points mid way along the top edge and and the bottom edge, respectively.

Now imagine that this square forms the bounding box for the feature being drawn (or the current map window, if in “viewport” coordinate mode). The default reference points mean that the gradient will be drawn from the middle of the top edge to middle of the bottom edge of the feature. Reference points of (0, 0) and (1, 1) would mean the gradient is drawn from the top-left to the bottom-right. Similarly, reference points of (0.5, 0.5) to (1.0, 1.0) would draw a gradient from the middle of the feature to the bottom right (good for radial gradients).

Example gradient reference points

There’s also the option to set either of the reference points as the feature centroid, which again can come in handy for radial or conical gradient types.

Gradient spread

If you’ve got your head around the reference points concept, then the next setting for gradient fills affects how the gradients spread. This takes effect whenever a gradient starts or ends before the bounds of the feature. The default setting of “pad” means that the gradient will simple “pad” out any extra space with the start or end gradient colour:

Gradient "pad" spread

“Pad” spread – notice how the darker blue is stretched across the right side of each feature

Repeat” mode will tile the gradient across the feature:

Gradient "repeat" spread

“Repeat” spread

Finally, “reflect” mode will draw a reflected version of the gradient to fill up any extra space:

"Reflect" spread

“Reflect” spread


Last of all, there’s a simple “angle” parameter, which allows you to rotate the entire gradient fill. This option is included mostly for use with data defined symbols, since a similar effect can be achieved by changing the gradient reference points. Amongst other effects, this is useful for achieving a “sun glint” on water, where each gradient is drawn in a random direction (more on this in a later blog post):

Data defined gradient angles

Random data defined gradient angles

This leads me into my final note… all of these properties can be data defined! So you could have a column in your data controlling whether each feature is drawn with a radial or linear gradient, or whether the gradient in a given feature should be drawn at a specific angle, or that the gradient in a feature should start at the centroid and end at the top right of the feature!

I’m excited to see what the QGIS user community is able to create using this new gradient fill feature when 2.2 is released. If you’ve already had a chance to play with the dev version of 2.2 and have something to show off, make sure you submit your map to the Flickr QGIS Map Showcase!

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