How to make a growing mesh

I am making a 2D map game where you are looking at a map and it starts from the dawn of time, and I would like it to be able to spawn a mesh (that acts as a civilization growing) that can only spawn if touching a game Object with the tag "land" and slowly expand over time, but stop when it hits the tag "water" for the collisions, I am using 2D collider triggers with the tags . If anyone has any ideas on how to make this work, feel free to respond, Thanks.