Hi guys, I have read all forum topics about grids, and still can´t have a clear answer, so here I am, asking again 
First, sorry about my English, I´m from Brazil…
I´m working on a City Building game, it´s online, so all changes are validated by the server.
What we do now is, I create a grid using a script that create several squares side by side, for example, let´s use, 10 by 10 squares, which give me 100 grids. I save this on a prefab, called grid, and put it on the map.
On runtime, to create a building, you click the button on the menu, and go over the map, it highlight the squares that you can build on green, and the ones you can´t red… when you click it, the selected object is instantiate on the position of the square (grid), and it updates on the server, that square X, have building Y.
It´s the same when you login in the game, it goes on the server, and check to put the buildings on their specific locations.
This worked so far, because it´s a small test map, but now we´re doing larger terrains, with several grids, so it came to millions of squares on the grid… so it´s like, building X on square 564.234.122
Not so good… I´m sure there is a better way to do that?
It´s much like Simcity, so the grid needs to have some info on it, like pollution, if has water, etc…
I don´t see how I can do this, without use tiles… do you guys have a better idea???
Many thanks and regards.