My third mini article about level building.

Edges

An Edge is where a Place or Path ends and another Place or a Path begins. An Edge is a doorway, a drop-off, a corner, a shield door, a hill that obscures sight to a neighboring Place. This is where the callout for your location changes, when you are no longer in the base, but behind the base. When you are not on the cliff, but below the cliff. No longer in the dish, but beside the dish. Not on the ramp, but on the bottom floor.

Edges naturally exist, you almost never have to put thought into creating an Edge, because if you have and number of Places or Paths, then you already have Edges. So then why even bother talking about them? It's useful to consider Edges when thinking about how a map will be played. For instance, when a player crosses an Edge, he should be in a different situation and should have different options. On Hemorrhage, the big hill in the middle of the map is an Edge between the two halves of the map. You don't have to worry much about anyone on the other side of the Edge, and at any point in the game, threats will be different on each side of the Edge. Think about when there is one Wraith on Hemorrhage. When it crosses the Edge, things change.

Once you’ve determined where your Edges are, then you can more easily flesh out what your battlefields (Places) will play like. For the most part, battles will take place within the same Place. Of course there are exceptions (like when there's a long sight line for a sniper that leads way down a long hallway and into another room), but generally players will tend to fight with other players in the same Place. Knowing this, you can more easily decide what weapons to make available, and what types of cover should be where.

Another thing that should be taken into consideration with Edges is how you can use them to introduce a new Place. When a player comes around a corner (which is an Edge), the designer has complete control over what is immediately visible. Use these "reveals" to your advantage. Whatever information you want to convey to the player about a Place is best done when the player is coming through an Edge to get there.