Calculating polygon area in QGIS without adding new field

Question

Is it possible in QGIS to quickly calculate the area of a polygon using a Processing tool, plugin, script without adding attributes or creating a new layer?

Something launching the results window or even a point and click feature?

Answer 1

The identify tool does offer you this information.

Click any feature, then expand the topmost dropdown menu. Here all basic geometric information is hidden, incl. the area and circumfence.

Answer 2

Create a label with the expressin $area (I should have used round($area)):

Answer 3

I personally find the identify tool sometimes too clunky. Here another approach:

To show the area for a polygon without using an additional field, you can just use a formula for a label with the $area function, e.g.:

round($area/10000,1)

will give you the area of the features in hectares.

As you just want to see the area when pointing/clicking, you could add

CASE
WHEN  is_selected() THEN round($area/10000,1)
END

When you now use the select tool pointing on a polygon, it will show the area label.

In case your polygons already have a label based on some field(s), you can extend the formula with an ELSE statement to switch between normal view and selected view:

CASE
WHEN  is_selected() is FALSE THEN "id"
ELSE round($area/10000,1)
END

Please mind that I never have used this approach myself, I just came up with this idea while reading your question.

Answer 4

Also possible by means of PyQGIS.

def feature_area(selected, _, __):
    n = len(selected)
    
    if n == 1:
        g = iface.activeLayer().selectedFeatures()[0].geometry()
        print("The area of selected feature is " + '{:0,.2f}'.format(g.area()) + " m²")
        
    elif n > 1:
        print("Select only one feature")

iface.activeLayer().selectionChanged.connect(feature_area)

Inspiration was found in: Determining number of vertices of selected object in QGIS 3

Answer 5

Another option is using the "Display" through RMC > Properties > Display.

Paste the following expression format_number($area,2,'de') into the 'Display Name' and press Apply.

Note: I made it in very intuitive way, more sophisticated output can be achieved via the 'HTML Map Tip'.

After hover over the feature and get the output