Terraforming Mars · Board game rules
Can I place a city on any hex, or are there placement restrictions?
Quick answer
No — city tiles cannot be placed on ocean-reserved or special reserved areas, and cannot be placed adjacent to another city tile (except Noctis City).
Details
When placing any tile, you must first check for placement restrictions: ocean-reserved areas (blue) are only for ocean tiles, and no other tile may go there, while special reserved areas are set aside for specific unique cities [p.4 — GAME BOARD]. Beyond that, city tiles specifically may not be placed adjacent to another city tile — the sole exception is Noctis City, which must always be placed on its own reserved area regardless of adjacency [p.5 — TILES].
Aside from these restrictions, you may place a city tile on any other available area, and you place a player marker on it to show ownership [p.5 — TILES]. If the area has a placement bonus (resources or cards), you collect that immediately, and you also gain 2 M€ for each adjacent ocean tile already on the board [p.5 — TILES]. At game end, each city scores 1 VP for every adjacent greenery tile, regardless of who owns that greenery [p.5 — TILES].
Watch out: Some project cards may add further specific restrictions or effects for city placement (e.g., the unique Capital tile), so always check the card text for any additional rules beyond the standard ones [p.5 — TILES].