Derived Properties

Some properties can be read but cannot be directly changed even though the Item is editable. This is because the property is a derived property.

For example all Polygon items have an Area property which tells you the item’s area in square metres.

The only way you can change the value of Area is by editing the geometry of the item.

Many system properties are derived. However user attributes are always editable and you can always change their values directly.

Here is a complete list of Point, LineString and Polygon Item properties:

TIP: See also Overlay Properties.