How to detect if an Actor is IN or OUT a closed Spline?

[Everynone]

Same question?

How to get a grid system in a closed spline for a city builder game?

Do you know how I can fill the inside of a closed spline with a grid system. My Idea is that I can easily change the spline and my grid system changes with it. Also important to say is that the player shouldn´t be able to place buildings out of the spline and the player is only able to place buildings in the closed spline.