Putting a unit on a tile, OR putting putting a city directly adjacent to the tile will achieve the same effect. You probably never noticed b/c you’re nearly always claiming all the tiles with units ASAP and the cities come much much later.
I played the campaign missions to the end for Tyranids and Space Marines. I played some conquests as Imp Guard and Necron. I still suck at Orkz.
Edit: The campaigns are okay lore wise, they’re kinda just full of spawning gotcha’s mechanically though.