There are a million random encounter generation tables online. We've even made our own. But there are some questions encountered when creating an encounter. When does the encounter begin? How do the NPCs feel about the PCs? Where are they on the map?
Thus cometh the Encounter Generation table, a table used to answer a few basic questions about the encounter. Roll the dice and see how close the encounter begins, how the NPCs feel about the PCs, how much fight they have in them, and how they're arranged on the map.