The theme in the example is divided into five classes (Havflate/Sea level, Små innsjøer/Small lakes, Større innsjøer/Larger lakes, Skog/Forest, and SnøIsbre/Glacier), each class with a separate fill color (Fill color). Glacier also has a stippled outline (Outline Color, Width, Pattern).
To define polygons for the different classes, this example uses a combination of Classitem and adding both column and attributes to the expression (Expression). For Classitem, the column “Objtype” has been selected. For the four simple classes – Sea level, Forest, Glacier – expressions (Expression) that only require a single column, such as “Sea level”, are set. A expression type is also defined (Expression type) – in this case, the type is “String”.
The values are obtained from the attributes column “Objtype” of the relevant data set.
For the two classes for lakes (Small lake and Larger lakes), we’re using the type (Expression type) “Logical expression”. It allows us to combine expressions (Expression) for a better specification. Example:
- Small lakes: ‘[objtype]’=’Innsjø’ AND [shape_area] < 100000000
- Larger lakes: ‘[objtype]’=’Innsjø’ AND [shape_area] > 100000000
Columns, comparison operators, and values are set. Square brackets “[ ]” are used to enclose the column names. If the column is of type Text, both column name (including the square brackets) and the attributes are enclosed using single apostrophes.
In the example above we’ve used the comparison operators =, < and >.
Below is a screenshot for each class (two images for the double class Glacier).