Operators used for class or ID columns
Columns that have a class or ID domain can also be used in formulas. When using
class names or IDs within an expression, these class names and IDs should be put
between double quotes, e.g. “Residential”. This also applies to the undefined
value “?” in class and ID maps or domains.
The number of operators and functions that you can use for class or ID columns is
quite limited. Of course, arithmetic operators make no sense (you can hardly divide
one word by another). Relational operators are only limited to two: = (check whether
two names are equal) and (check if they are unequal). Logical operators and conditional
functions, however, are used extensively on class or ID columns.
Some examples are shown below. The first example is finding out which city blocks
have a land use Residential and occur within the district nr 7.
The result of this formula is a column, using domain Bool.
Now let us combine several operators and an IFF function. We will find out the city
blocks with either a residential or commercial land use in district nr 7.
Note that in the Column Properties dialog box the suggested domain of the output
column is City_Landuse. This is because the possible results of the formula are
either Residential or Commercial, which are both items of the domain
City_Landuse, or ? (undefined).