My aim at such outdoor events is to have as many people participate as possible, regardless of the size of the dance floor. In fact, if it's a party of 150-200 people, and it's going to be under a large tent, I encourage the wedding couple not to get a dance floor if ours is the only dancing. Participants at such events don't do a buzz step swing; they'll be just as happy to walk/hop around their partner with an elbow swing. I'll call simple dances-- rarely any that are actual contras in lines-- that allow maximum participation with minimum instruction. Having the dance floor in the center can send the wrong message that this is only for the few people who can squeeze onto that space.
And if that decision has already been made and there's a floor there, then simple longways dances (such as Galopede) can and do extend off the floor allowing many more to participate. A Sicilian circle such as Haste to the Wedding can go all around the open space in the tent, crossing over the official dance floor as needed but not limited to that space. David Millstone Lebanon, NH
