Executing original features of merged layers using QGIS

Question

I am using QGIS 3.10.

Following this query:

QGIS 3.10 problem with merging layers & multipart promotion

I've managed by merging the layers featuring the same geometry. Unfortunately, the effect is not enough for me, since the newly merged layer contains its own feature (especially with styling).

Basically I merged two layers with completely different styling, as per below:

but my merged layer has its own stylisation, as it worst only 1:

I want to have the layers merged, but with the original styles kept.

Is it possible?

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I tried to categorize these layers as per the image below:

creating the custom styles in the "categorized section". Unfortunately in the effect, my shape disappeared.

I don't know how to do now. I set "Area" as a value, although I noticed, that my object is gone once I switch on the "Categorized" option.

Answer 1

Short Answer: No, not as far as I know.

Long Answer:

You can copy style from one layer to another through the right-click interface. But this only works for one layer at a time. If you do it for both of the original layers, the style from the second layer will overwrite the style from the second layer.

To get two different styles for different features in the same layer, you need a Categorized Style. As far as I know there's no way to copy style from one layer into a single category of another layer. That would be a cool feature though. There are already some outstanding Feature Requests for improvements to the copy/paste symbology ability. For example: Smarter Style Copy/Paste #29541. If none of the existing requests ask for what you want you could post a new request.

Here's how to do it manually:

You will need to set up categorized styling. This requires that the features have an attribute telling you which layer they came from. For example, it could be an attribute called "source" which has the values 'layer1' or 'layer2'. Any existing attribute that makes the distinction will suffice.

Then manually set up the style from each of the source layers separately for each category.

Note: you can re-use a color by saving it in the color selector widget. Click on the color at the bottom of the widget where it says "current" and drag it over to one of the empty boxes in the bottom-right part of the widget. Now that color is temporarily saved, and you can select it from that box when you choose the color for another layer.

Answer 2

The method you use in the updated section of your Question is OK, you now only need to tell QGIS to apply the Categorized style taking into account the Area field of your layer: