Filtering Features in Mergin Maps Mobile App

• Enable and define filtering in QGIS
  • Filter types
• Filtering features in the mobile app

Custom filters can be added to the mobile app to easily filter features displayed on the map as well as in the survey layers.

Feature filtering blog

You can read about this feature also on our blog From wishlist to app: Feature filtering is live.

Enable and define filtering in QGIS

Filters can be enabled and defined in QGIS in Project Properties for GeoPackage layers.

Plugin upgrade

If you do not see the Filtering option in the Project properties, check for plugin upgrades.

Check the ✔️ Enable filtering option in the Mergin Maps tab, click on the Add filter button and select a filter type from the list. The list of available filter types and their properties can be found below.

Then, define the filter:

• Type - the filter type (in general, it should match the widget type of the filtered field)
• Layer - choose from the project's GeoPackage layers
• Field - choose from the fields of the layer. Only fields with data types compatible with the selected filter type are offered.
• Title - the name of the filter, which will be displayed in the mobile app

You can add as many filters as you need by using the Add filter button.

The order of filters can be changed by selecting a filter and using the Up and Down buttons. To remove a filter, select it and click the Remove button.

Don't forget to save your project and synchronise changes so that you can use the filters in the mobile app.

Filter types

Text filter uses simple text input. Results are filtered based on the SQL expression "field" ILIKE '%input%'. Available for text and number field types.

Number filter provides from and to number inputs. Results are filtered based on SQL expression "field" >= 'input_from' AND "field" <= 'input_to'. Available for text and number field types.

Date filter provides from and to date (calendar) inputs. Results are filtered based on SQL expression "field" >= 'input_from' AND "field" <= 'input_to'. Available for date field types configured with the Date and time widget.

Boolean filter provides a toggle between all, true and false values. Results are filtered based on SQL expression "field" == 'input'. Available for Boolean, text and integer field types configured with the Checkbox widget.

Single select filter provides a drop-down menu of field values. One value can be selected at once. The results are filtered based on SQL expression "field" == 'input'. Available for all field types. Note that Value relations with multiple selections are currently not supported.

Multi select filter provides a drop-down menu of field values. Multiple values can be selected at once. The results are filtered based on SQL expression "field" IN ('input'). Available for all field types. Note that Value relations with multiple selections are currently not supported.

In the mobile app, the filters look like this:

Filtering features in the mobile app

Filters defined in Mergin Maps project in QGIS can be used in the mobile app. You can filter features across multiple layers by entering or selecting values in corresponding filters. The filtering affects both the map display and the feature browsing list.

Filters do not stay saved when the app is restarted.

Here is an example of how filtering works:

1. Tap the More button to open Filters defined in the project

   Filtering has to be enabled in the QGIS project, otherwise this option is not displayed.

2. Enter or select values in the filters. You can use more filters at once.

   Here, we will use a Single select filter on the trees layer and select a tree species value from the list.

   Tap on the Apply filters button to confirm the filtering.

3. With active filters, only features that match the criteria are displayed on the map as well as when browsing features.

   You can use the active Filters button to quickly access filters.