“Expressions offer a powerful way to manipulate attribute values, geometry and update the symbology of layers.”
Attribute defines the characteristics of an entity. In some cases, the attributes can contain fields that allow users to dynamically change the geometry style, the content or position of the label. Expressions allow users to manipulate the attribute data and compute values on the fly that can be utilized in styling layers, labelling and updating columns.
In this module, we explore how to construct expressions to manipulate data and use it update values in columns in new columns or existing columns.
Goal: To learn how to use expressions to manipulate data
You should produce an attribute table that has an extra column road_length
Expressions are extensively used in QGIS and in order for a user to become a power user, they should master them. In QGIS there is an option to write custom expressions to expand on the predefined expressions available after installing QGIS. The type of data determines the kind of expression to use. For example, if the data is numeric users might need to use mathematical expressions whilst if the data is of string type then users might need to use string expression.
Click here to download the sample data for the lesson.