Displaying differently styled features from within a single shapefile in QGIS

Question

I am using QGIS 3.22.1. I have a single FEMA NRI shapefile layer in my project that contains many 'features' (aka columns in the attribute table). For instance, there are columns for risk of drought, hurricanes, and other natural disasters. I know how to pick off a specific feature and create a style to display it nicely on the map. But, I want to be able to apply different styles to several more of these features and then easily toggle between or even turn them on simultaneously.

In the left side layers panel, I'd like to see something that emulates this:

|_|FEMA Shapefile Layer
    |_| Drought Risk
        -> Categorized Style Classification
    |_| Hurricane Risk
        -> Categorized Style Classification
|_|Other Shapefile Layer(s)

Then I want to be able to be able to select and show Drought Risk, Hurricane Risk, or both on top of each other, hopefully with simple checkbox toggles.

Is the best way to do this to simply duplicate the layer and apply a different style to each of the copies?

Answer 1

Sometimes the simplest answer is the best one, and you already identified it.

Is the best way to do this to simply duplicate the layer and apply a different style to each of the copies?

Import the layer into the map as many times as needed using the same source and theme each layer. A layer should generally only have one function and therefore one theme. Using the same source, will ensure that all the layers will have the most up-to-date information and each thematic layer can be easily toggled.

You can use QGIS' Content Groups organize and allow you to toggle the visibility of all layers.

Answer 2

The so called "Styles" the best solution for this. Right-click your layer and "Add..." a new Style (you can also rename the currently selected style there, e. g. from "Default" to "Drought Risk").

Then you can set up this new Style's symbology in any way you like and easily switch between them.

By using this approach you have a well setup project, these Styles can also be used in Layouts or Map Themes in a straight-forward way.

Answer 3

To define different styles based on conditions from attribute values, use styling with Rule based renderer (see docu). You can achieve (almost?) everything you could do with other methods.

You can add as many styles as you want and define for each simple or complex conditions when it should be visible. It will be still one layer only, but with many different styles.

Basic settings

In the layer panel as well as in the Layer styling, you can activate and deactivate each style by clicking the checkbox next to it: see the red arrows in the screenshot.

One layer, styled with four different styles, here based on a filter condition (Rule) based on the polygon's Name attribute - you could include other attribute fields to create complex conditions:

Use with scalar attributes: data driven override (manual)

If you have scalar attributes and want to get a graduated style based on the attribute value, you can use data driven override for any part of the style like color, fill style, stroke width, stroke style etc. Set a rule based renderer and then in the style settings, click on the data driven override icon at the right side of the setting options and click on Assistant:

Then select a source (be it an attribute field or a more complex expression), load min/max values (or enter them manually) and select a color ramp to get a graduated style.

Graduated style: solid fill with a white-to-blue color ramp, based on the attribute value (see label for the value for each feature); Storke color and stroke width (border of each polygon) similarily styled based on the same attribute:

Refine selected rules to create categorized or graduated styles (automatic)

You have even more options selecting one rule defined style by selecting one of the three options under Refine selected rules (right click rule or open it at the bottom of the panel, see screenshot). Here, you can, between elso, choose Add categories to rule or Add Ranges to rule to create a style that corresponds to Categorized or Graduated layer style rendering.

Graduated style based on the attribute value, but only for features with value > 50. I used Add ranges to rules with the expression scale_linear( value,50,100,0,100) to "spread" the color ramp (use the full spectrum of the white-to-red color scale) for values from 50 to 100: