Awareness maps in QGIS
When an issue is relatively new, it is often useful to go through an awareness-raising phase. Maps play a key role in this process: they reveal worrying facts and draw the attention of the public or decision-makers to an issue.
In QGIS, an effective awareness map generally uses divergent symbology. The idea is to center the representation on a reference value (average, median, zero, policy target, etc.), then highlight values above and below this threshold.
A bright color (e.g., magenta, red, or intense blue) can be used to immediately draw the eye to critical areas.
Example: Magenta polygons on a map can represent areas where the poverty rate is significantly higher than average.
The “Above and Below” theme in QGIS
The equivalent of the Above and Below style in ArcGIS Online can be reproduced in QGIS with a color gradient centered on a key value:
- Define the central value: statistical mean, median, or a known threshold (e.g., zero, public policy target, legal value).
- Define high and low classes: using a standard deviation, quantiles, or custom thresholds.
- Apply a divergent three-color palette:
- a bright color for high values,
- another for low values,
- a neutral color for values close to normal.
For points and lines, you can combine proportional size and divergent color to highlight not only the deviation from the reference value, but also the relative importance of each entity.
When to use this approach?
Choose this type of map when you want to anchor the reading around a clear reference value, in order to show:
- which areas are performing better than expected,
- which areas are struggling,
- and which areas are within the norm.
Example: for traffic data, you can highlight areas where volume is above or below the observed average, making it easier to identify problem areas or, conversely, areas of success.
Create the AboveAndBelow color gradient
The palette ranges from green to magenta to yellow. To create it:
– Copy and paste the following code into a file named aboveandbelow.xml
<!DOCTYPE qgis_style>
<qgis_style version="2">
<symbols/>
<colorramps>
<colorramp type="gradient" name="AboveAndBelow" tags="Colorful,AboveAndBelow">
<Option type="Map">
<Option value="69,146,21,255,hsv:0.26974999999999999,0.85304036011291673,0.57334248874647131,1" type="QString" name="color1"/>
<Option value="248,247,207,255,hsv:0.16225000000000001,0.16768139162279697,0.9739070725566491,1" type="QString" name="color2"/>
<Option value="ccw" type="QString" name="direction"/>
<Option value="0" type="QString" name="discrete"/>
<Option value="gradient" type="QString" name="rampType"/>
<Option value="rgb" type="QString" name="spec"/>
<Option value="0.504808;221,238,209,255,hsv:0.26338888888888889,0.12065308613717861,0.93389791714351111,1;rgb;ccw:0.997596;231,25,178,255,hsv:0.87608333333333333,0.89083695735103385,0.90663004501411459,1;rgb;ccw" type="QString" name="stops"/>
</Option>
</colorramp>
</colorramps>
<textformats/>
<labelsettings/>
<legendpatchshapes/>
<symbols3d/>
</qgis_style>
Open the QGIS style manager.
Use the Import/Export button to select the aboveandbelow.xml file and load the color gradient into your QGIS installation.
Apply this symbology to a polygon layer
QGIS does not allow you to directly define a “ramp” symbology equivalent to that used for rasters for vector layers.
However, you can create it by using the “single symbol” type with a “simple fill” and assigning a color expression to it:
AboveAndBelow expression
The goal is to apply the color gradient to an attribute field (here field_name). You will need to adapt it by replacing it with the actual name of the attribute field.
The expression calculates the mean and standard deviation of the values in field_name on the fly and adjusts the gradient by assigning the value 0 to the mean-standard deviation and 1 to the mean+standard deviation.
ramp_color('AboveAndBelow',
scale_linear(
"field_name",
mean("field_name") - stdev("field_name"),
mean("field_name") + stdev("field_name"),
0, 1
)
)This means that:
- all polygons with a value equal to or less than the mean-standard deviation will be green
- all polygons with a value equal to or greater than the mean+standard deviation will be magenta
- polygons between these two values will have a graduated color
