Updating fields using values from other layers

When creating a new feature in Roam you can pull values from another layers using a default expression on the field.

Setup the default expressions using the config manager

  • Open Config Manager
  • Select the Project and Form
  • Select the field
  • Update the expression tab to be Capture value from field
  • Set the Capture Layer to the layer to take the value from
  • Set the Value Field to the field which has the value you need
  • Set the Expression to a QGIS expression that will test if to return the value or not


Common Expressions

  • intersects($geometry, buffer($roamgeometry, 5))
  • within($geometry, buffer($roamgeometry, 5))

$roamgeometry is a reference to the currently selected feature when the expression is run. This is the feature being edited or created when the form is opened.

How it works

When Roam creates a new feature the expression is tested against every feature within view to see if the expression will match.

Note: The first matching feature is used for the value and there is currently no UI control to pick other values