Can't pass a certain area for Rpg Maker XP Help needed(RESOLVED)

Hi,
Does anyone know how to make it so that the hero can't get pass the grass but must stay on the road. In other words, the hero can't get pass a certain tile. I'm pretty sure you would use a common event and with variables. I'm not sure, but I think it might relate to having battles in only grassy area like in those pokemon games. I remember seeing it one time so if you have a link to that, can you please post it?

Thank you,
Theodie12345

You want a tile simply to be unpassable? 

All you have to do is open the database, click Tileset, and set the passability on the tile you want unpassable to X.

Wasn't what I meant, but I figured out something else using what you were telling me about. Thanks for the advise.