I have several symbol layers:
current: "from" <= 1832 AND "to" > 1832 former: "from" <= 1832 AND "to" <= 1832 future: "from" > 1832
What I'd like to do is be able to change 1832 to another year without separately editing each rule. Ideally I'd be able to define a variable somewhere and refer to that variable in the rules.
I've found a workable solution by creating an extra column in the attribute table and filling it with 1832, then referring to that in the rules. It's easy to change with the field calculator, but is rather inelegant. I tried using a joined table and editing that instead, but it doesn't update the rendering properly when I save the table with a new year value.
Is there a better way to do this, or have I determined the optimal way?