[GIS] Showing feature count for layout extent on legend using QGIS

Question

I'm using QGIS 3.6.1 on Win10.

I have a print layout with a map of an area within my total work data set.

I add an item to the print layout legend with the summation button on for "Show feature count for each class of vector layer." I expect this to show the count of the features visible within the layout map extents. Instead, it shows the total count for the entire data set.

Is there a way to just count the data within the map layout extents and show this on the legend?

Answer 1

I would expect the option "filter legend by map content" to cause the "filter count" to be limited to the features within the map extent. But you're right, the "feature count" is not filtered by the map extent.

This seems like a bug, so I made a bug report. Visit the bug report page to check on the status of having this bug fixed, but don't expect it to happen immediately. This is a pretty minor issue and the QGIS devs have a lot on their plates. In the meantime, try out the workaround below.

How to use expressions in a label item to display a count of features within the map extent:

This expression returns the map extent as a polygon: map_get(item_variables( 'Map1'),'map_extent'), where Map1 is the Id of the map. You have to define the Id of the map item in the Item properties panel.

Use the aggregate(count) function to count the points in a given category that intersect the map extent. The following example will count the points in the map canvas that have the value 'Group A' in their "category" field.

aggregate( 'New scratch layer','count',"category","category"='Group A' AND intersects($geometry,map_get(item_variables( 'Map1'),'map_extent')))

Repeat for each category.

Note: If you want a simple (uncategorized) count of all the features on your map, use this expression: aggregate('New scratch layer','count',"category",intersects($geometry,map_get(item_variables( 'Map1'),'map_extent')))