Thanks for playing, glad you enjoyed the machine gun crossbow!
Level 10 was the end of the game for quite a while during development so way to go on reaching that point!
The map gives an overhead view of the surrounding area so you can see where ogres are approaching from, and the guards allow you to sound an alarm to kill any ogres that get past you before they get to the village.
In theory you can transition to a different mode of play later in the game by investing heavily in guards after unlocking the map and using them to kill all of the ogres instead of using the crossbow. It's very challenging to get to that point though.