It's a question of scope, nothing more. Tactics are the means to win a battle. Operational considerations might be more accurately described as the means to win a campaign. Strategic considerations are the ends.

To use a simple analogy, the strategic bomber campaign the Allies unleashed on Germany in WW2 had a strategic objective - crush Nazi war production. The operational considerations included how many planes to send where, on which routes and so on. Tactical considerations would encompass things like formations of the bombers, evasive maneuvers and technical innovations to keep bombers alive.

Since Rome doesn't have provinces with fixed terrain types, rather wherever the two army icons meet on the 3D map is the terrain the battle is fought on, it becomes an operational consideration. Launching an invasion is strategic - seize some economic resources or destroy threatening enemy forces on the border (or whatever). Strategic = objective. Operational = how to meet that objective.

The lines are kind of blurry/subjective anyways, so the terms aren't really all that important.