Styling and symbology

Before we begin

Before diving into this module’s exercises, it would be good if you can review and familiarize yourself with styling layers and making maps. You can also look at advanced styling and symbology techniques.

NOTE

For exercises in this module, you will use the bnhr_qgis-architects-planners-urban-002.gpkg inside the data subfolder in the BNHR_QGIS-for-Architects-Planners-and-Urban-Practitioners folder.

This geopackage contains all the data and projects associated with the exercises.

Multi-variable symbologies

1.1. Bivariate choropleth map of barangays showing population density and annual population rate

Level: Intermediate

PRO-TIP

For our training participants, you can load the completed/styled layer by loading the bivariate-choropleth project found inside bnhr_qgis-architects-planners-urban-002.gpkg.

What we want to achieve

1. A map of Quezon City barangays showing both the population growth rate (2000 to 2020) and the people per 100 square meters.

What we have

1. adm_brgy_quezon_city_pop2000_2020 - the barangay-level admin boundary data generated from a previous exercise with population from 2000 to 2020

Relevant QGIS knowledge/skills

• Blending modes
• Bivariate choropleth maps
• Expressions

Steps

1. Load the adm_brgy_quezon_city_pop2000_2020 layer. Make sure that it already has the fields for population from 2000 to 2020.

Attribute table of adm_brgy_quezon_city_pop2000_2020 showing population data from 2000 to 2020

2. Duplicate the adm_brgy_quezon_city_pop2000_2020 layer. Since we’ll be creating a bivariate choropleth map using blending modes, we need 2 vector layers to show. In this case, we’ll show the annual population growth from 2000-2020 and the number of people per 100sqm in the barangay. Name the two layers brgy_rate and brgy_popden.

NOTE

To duplicate a layer, right-click on the layer ‣ Duplicate layer.

brgy_rate and brgy_popden layers

3. Next, we make a choropleth map for the brgy_rate layer using a Graduated symbology using the following parameters.

   • Symbology: Graduated
   • Value:

     (pop2020-pop2000)/20

   • Classes
     • Low
       • Color: #e8e8e8
       • Values: -500.00 - 0.00
     • Moderate
       • Color: #dfb0d6
       • Values: 0.00 - 500.00
     • High
       • Color: #be64ac
       • Values: 500.00 – 5000.00

PRO-TIP

Notice the Expression icon () to the right of the Value parameter.

This means that we can directly use the Expression computing for the annual population growth from 2000 to 2020 ((pop2020 - pop2000)/20) without needing to create a new field on the layer.

Style parameters for brgy_rate layer

4. Your brgy_rate layer should look like:

Choropleth map for brgy_rate layer

5. Do the same for the brgy_popden layer but our parameters will be:
   • Symbology: Graduated
   • Value:

     100*pop2020/$area

   • Classes
     • Low
       • Color: #e8e8e8
       • Values: 0.000 - 1.500
     • Moderate
       • Color: #ace4e4
       • Values: 1.500 - 3.000
     • High
       • Color: #5ac8c8
       • Values: 3.000 - 15.000

Style parameters for brgy_popden layer

6. Your brgy_popden layer should look like:

Choropleth map for brgy_popden layer

7. Now that you have the two choropleth maps, create the bivariate choropleth effect by changing the blending mode of the top layer (brgy_popden) to Multiply.

Setting blending mode of brgy_popden layer to Multiply

Bivariate choropleth of the population growth (2000-2020) and population per 100sqm in Quezon City barangays

PRO-TIP

You can use the Bivariate legend plugin to create a legend for the map you created.

The Bivariate legend plugin

ANOTHER WAY TO CREATE BIVARIATE CHOROPLETH MAPS

There’s a plugin called the Bivariate color polygon renderer that adds an implementation of a bivariate color renderer directly for a polygon layer’s styling options.

Try to use this plugin and check what the pros and cons are of this approach vs the approach we took.

1.2. Using both size and color to communicate information about the districts

Level: Intermediate

PRO-TIP

For our training participants, you can load the completed/styled layer by loading the size-and-color project found inside bnhr_qgis-architects-planners-urban-002.gpkg.

What we want to achieve

1. Use circles to show population information about districts in Quezon City where the size pertains to the people per 1000 sqm and the color indicates the annual population growth from 2000 to 2020.

What we have

1. adm_dist_quezon_city_pop2000_2020 - the district-level admin boundary data generated from a previous exercise with population from 2000 to 2020

Relevant QGIS knowledge/skills

• Data-defined overrides
• Expressions
• Geometry Generators

NOTE

As with most things in QGIS, there are several ways to approach this problem in order to arrive at the same outcome. Here, I will show two options:

1. A straightforward option using geometry generators and data-defined overrides that do not require the creation of a new field or a new layer.
2. An option that requires creating a new field (pop_per_1000sqm) and a centroid layer then applying a graduated symbology with data-defined overrides.

Option 1 - Geometry generator approach

1. Load the adm_dist_quezon_city_pop2000_2020 and duplicate the layer.
2. Rename one base and apply a simple single symbol symbology.
3. On the other layer, selece Geometry Generator as its Symbol layer type.

Selecting Geometry Generator as Symbol layer type

4. Change the Geometry type to Point/MultiPoint and use the following expression to generate a centroid:

   centroid(@geometry)

Creating a point geometry using the centroid expression

5. On the Simple Marker, use the Assistant to override the Size parameter.

Selecting the Assistant

6. Use the following parameters:
   • Source

     1000*pop2020/$area

   • Values from 10 to 35
   • Output
     • Size from 500
     • to 3500

Symbol Size parameters for the Assistant

7. Your layer should now look like below:

District layer styled as differently-sized points

8. Next, let’s use the Assistant to override the Symbol Fill and Symbol Stroke Color parameters.

Symboll Fill Color parameters for the Assistant

Symbol Stroke Color parameters for the Assistant

Option 2 - Centroid approach

1. Add a new field to the adm_dist_quezon_city_pop2000_2020 layer to hold the number of people per 1000 square meters using the following expression:

   1000*pop2020/$area

Creating the pop_per_1000sqm field using the Field Calculator

2. Run the Centroid processing algorithm to create a new point layer (centroid) based on adm_dist_quezon_city_pop2000_2020.

Parameters of the Centroid processing algorithm

3. A new layer (Centroid) should be created.

Centroid layer

4. Apply a Graduated symbology and use the following parametres:
   • Value: pop_per_1000sqm
   • Method: Size
   • Size from: 500 to 3500 Map Units
   • Classes:
     • 10 - 15
     • 15 - 20
     • 20 - 25
     • 25 - 30
     • 30 - 35

Graduated symbology using size for the Centroid

5. Your Centroid layer should look like below:

Centroid with size-based Graduated symbology

6. Use the Assistant to override the Symbol Fill Color with the following parameters:
   • Source:

     (pop2020-pop2000)/20

   • Values from: 500 to 15000

Symbol Fill Color parameters for the Assistant

7. Your layer should look like below:

SOMETHING TO THINK ABOUT

How will you add a legend on the print layout to reflect this multi-variable symbology?

Rule-based and scale-dependent symbologies

2.1. Styling roads and land-use using rules and symbol levels

Level: Intermediate

PRO-TIP

For our training participants, you can load the completed/styled layer by loading the rules-and-symbol-levels project found inside bnhr_qgis-architects-planners-urban-002.gpkg.

What we want to achieve

1. Style a road network similar in style to the ones we see in web maps by applying rule-based symbology on OpenStreetMap road data.
2. Apply the same symbology to multiple landuse categories.

What we have

1. adm_municity_quezon_city
2. osm_roads_quezon_city
3. osm_landuse_quezon_city
4. Other relevant layers:
   • satellite image basemap

Relevant QGIS knowledge/skills

• Rule-based symbology
• Symbol levels

1. Load the adm_municity_quezon_city, osm_roads_quezon_city, and osm_landuse_quezon_city layers.
2. Style adm_municity_quezon_city using Inverted Polygons and apply two fills (a Simple Fill and a Gradient Fill).

The adm_municity_quezon_city styled

NOTE

The Inverted Polygons symbology allows us to style the area outside the polygon instead of the polygon itself. In this case, this means that we’ll be styling all the area outside the adm_municity_quezon_city layer.

SOMETHING TO THINK ABOUT

How should your layers be ordered so that the roads and land-use features outside of Quezon City isn’t shown on the map?

Apply rule-based symbology to the road network data

1. For the osm_roads_quezon_city layer, you will create 3 rules—one for primary roads, another for secondary roads, and a catch-all (for everything else). The rules will be:
   • Primary roads:
     • Label: primary
     • Filter:

       "fclass" in ('primary')

     • Symbol:

       • Simple Line (1)

         • Color: #fff495
         • Stroke width: 40 meters at scale
         • Stroke style, Join style, Cap style: Solid line, Round, Round

       • Simple Line (2)

         • Color: #ecec32
         • Stroke width: 50 meters at scale
         • Stroke style, Join style, Cap style: Solid line, Round, Round

Rules for styling the primary roads (1)

Rules for styling the primary roads (2)

• Secondary and tertiary roads:
  • Label: secondary and tertiary
  • Filter:

    fclass in ('secondary', 'tertiary')

  • Symbol:

    • Simple Line (1)

      • Color: #fff495
      • Stroke width: 20 meters at scale
      • Stroke style, Join style, Cap style: Solid line, Round, Round

    • Simple Line (2)

      • Color: #ecec32
      • Stroke width: 30 meters at scale
      • Stroke style, Join style, Cap style: Solid line, Round, Round

Rules for styling the secondary & tertiary roads (1)

Rules for styling the secondary & tertiary roads (2)

• Other roads:
  • Label: others
  • Filter:

    Else

  • Symbol:
    • Simple Line (1)
      • Color: #ffffff
      • Stroke width: 8 meters at scale
      • Stroke style, Join style, Cap style: Solid line, Round, Round
    • Simple Line (2)
      • Color: #d3d3d3
      • Stroke width: 12 meters at scale
      • Stroke style, Join style, Cap style: Solid line, Round, Round

Rules for primary, secondary + tertiary, and other roads

However, if you zoom in to the map, you will notice a bit of an issue.

Zoomed in road layer. Notice the poor overlapping of the different features and symbols.

If you look real close, you will notice that the different road feature overlap in a poor way. What you want to do is control the rendering order so that the primary roads are rendered over the secondary and other roads while the secondary roads are rendered over the other roads. To do this, you can use Symbol Levels.

Rendering roads consistently and cleanly using Symbol Levels

Symbol Levels allow you to define the order in which the symbols are rendered. The numbers assigned to symbol rules define when they will be rendered, that means a lower number is rendered first and a higher number will be rendered on top of it. Using this, you can ensure that the other roads are rendered at the bottom and the primary roads are rendered on top.

1. Click Symbol Levels on the Layer Styling panel or the layer Properties of the osm_roads_quezon_city layer.

Opening the Symbol Levels dialog

2. Update the Symbol Levels for each of the rules. Make sure that the values for primary are the highest while the values for Others are the lowest.

Symbol level values for the road symbology rules

PRO-TIP

If you notice that your layer or features are overlapping poorly or not rendering in a way that you want, you can use symbol levels to fine-tune and configure which features should appear on top and which ones should appear on the bottom.

3. With these symbol level rules applied, your road layer should look like below when zoomed in.

Properly configured symbol levels for roads

Road network data styled using rule-based symbology with symbol levels applied

WHY DO WE NEED TO DO THIS

By default, QGIS follows the internal ordering of layer features when rendering them on the Map Canvas. If you are styling a road network consisting of roads at different levels/elevations (e.g. underpass, overpasses/flyovers, tunnels, etc,), this can lead to a visual mess that makes it hard for the map reader to understand the relative positions and relationships between the different road segments.

By assigning different Symbol Levels to different road layers (or even different features within a layer), you can ensure that roads at higher elevations are always drawn on top of roads at lower elevations.

Apply rule-based symbology to the landuse data

Activate the osm_landuse_quezon_city and notice that there are several land use classes available.

In this case, we want to style only the “green” areas. We can do this by applying a rule-based symbology.

1. Select the landuse layer.

2. Select Rule-based for the symbology type.

3. Add a new rule using the green arrow.

4. Use the following rule:

   1. Label: green
   2. Filter:

   fclass in ('farmland',  'farmyard', 'forest', 'grass', 'meadow', 'nature_reserve', 'orchard', 'park', 'scrub')

5. Add another rule as a catch-all. Style this catch-all as below.

PRO-TIP

You can combine/refine rule-based symbology with other symbology types (e.g. using categories, ranges, etc.). You can do this using the Refine Selected Rules function.

TRY IT

Aside from using rule-based symbology, you can also apply 1 symbology to multipule landuse values by merging categories when using a Categorized symbology.

Try to do this.

2.2. Showing different features at different zoom levels

Level: Intermediate

PRO-TIP

For our training participants, you can load the completed/styled layer by loading the scale-dependent-rendering project found inside bnhr_qgis-architects-planners-urban-002.gpkg.

What we want to achieve

For this exercise, your goal is to change which features and layers are shown as you zoom in or out of the map. In a way, you will be changing the level of detail in the map depending on the zoom level. For example:

• When zoomed out (e.g. scale < 1:50,000): you only want to see the primary, secondary, and tertiary roads as well as the green areas.
• At middle zoom level (e.g. scale between 1:25,000 and 1:50,000): you want to add the other roads as well as the flood hazard layer.
• When zoomed in (e.g. scale > 1:25,000): you want to show all layers including the osm_buildings.

What we have

1. adm_municity_quezon_city
2. osm_roads_quezon_city
3. osm_landuse_quezon_city
4. upri_quezon_city_floodhazard_100yr
5. ms_building_footprints_quezon_city

Relevant QGIS knowledge/skills

• Scale-dependent visibility
• Rule-based symbology
• Symbol levels

Scale-dependent visibility

The trick here is to use Scale Dependent Visibility. In QGIS, you can fine-tune and control the scale range at which layers and features become visible.

• For layers: you can find this in the Rendering tab of the Layer Properties
• For features styled using rule-based symbology: you can specify the minimum scale and maximum scale in the style settings.

1. Load the upri_quezon_city_floodhazard_100yr and ms_building_footprints_quezon_city layers and style them accordingly.

All layers loaded in QGIS

2. For osm_roads_quezon_city, set the following parameters for the others rule:

   • Min. Scale: 1:50000
   • Max. Scale: 1:1

   Don’t forget to apply your changes.

Applying a scale range to the others rule

Scale range showin in the rule-based symbology

3. Do the same for the non-green rule in osm_landuse_quezon_city but with the following parameters:
   • Min. Scale: 1:10000000
   • Max. Scale: 1:25000

SOMETHING TO THINK ABOUT

What do the Min Scale and Max Scale values mean for the osm_roads_quezon_city and osm_landuse_quezon_city layers?

4. For upri_quezon_city_floodhazard_100yr, open its Layer Properties and go to the Rendering tab. Check the Scale Dependent Visibility and put 1:50,000 as the Minimum.

Applying scale-dependent visibility on upri_quezon_city_floodhazard_100yr

4. Look at your map canvas. You should notice that when you are zoomed out (or when the scale is less than 1:50,000), the other roads and the flood hazard are not visible and when you zoom in (or once the scale is greater than 1:50,000) they appear.

“other” roads and the flood hazard do not appear at 1:90000 scale

“other” roads and the flood hazard appear at 1:30000 scale

5. For ms_building_footprints_quezon_city, do the same thing that you did for upri_quezon_city_floodhazard_100yr but put the Minimum to 1:25,000.

Take a look at you map canvas again, this time the building data should only appear when the scale is greater than 1:25,000.

Applying scale-dependent visibility on ms_building_footprints_quezon_city

Building footprint appear while non-green landuse disappear at 1:10000 scale

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