The ground stops being scenery
Cells are no longer interchangeable. Terrain, outposts and a border that has to be pushed one cell at a time — plus five things worth raising, and the guns to keep them.
Until now every empty cell in a system was the same cell. “Expand here rather than there” was not a decision anybody could get wrong, which meant it was not a decision.
Ground that is worth something, and ground that is in the way
Five kinds of terrain now sit under the map. Ore basins pay a mining station better than plain space would. A science anomaly is the only place a research station is worth building, and what it speeds up is the system it stands in — nothing else in your empire. A nebula yields nothing and hides what sits in it.
The other two are walls. A debris field blocks building until somebody pays to haul the wreck out. A gravity well blocks it forever, for everybody, and that is the most useful entry in the whole table: permanent walls are what turn open space into corridors, and a corridor is a front worth holding.
The rule we kept coming back to is that a terrain has to cut both ways or be an obstacle. A map made only of bonuses is a map where everyone wants the same cells and nothing else about the ground matters.
Borders you have to push
An outpost has to touch ground you already hold. Nobody drops a claim on the far side of a system any more, so borders are lines instead of confetti, and a frontier is somewhere you can actually be met.
Taking ground somebody else holds is a fleet’s job, not a builder’s. A cell can be garrisoned with a defense array, in which case the assault goes through the guns first, costs you ships, and leaves a report like any other battle. Winning does not hand the cell over either — a clock runs first, and it is long enough that the loser has time to come back for it.
Held, not owned
Jump gates, research stations and defense arrays work for whoever controls their cell, not whoever paid to build them. Taking someone’s gate is the same thing as having one.
Two things territory deliberately does not do, and will not start doing: it never blocks a fleet — being surrounded is a bad position, not a prison — and nothing it gives you is empire-wide. Every effect stays on its cell or in its system, so what you are playing is the shape of your territory rather than the size of it.