There is a chart in the original post giving details of what status each region is in throughout the war. After the rules and before the workshop settings.

Flanders divides into a north and south region. The south is a hotspot because of the Somme offensive, but the north is quieter as it is only medium. The Somme offensive will calm down in October before all regions except Verdun become quiet for the winter months, when campaigning becomes difficult.