The command is.connected(X) returns TRUE if the object
  X consists of a single, topologically-connected piece,
  and returns FALSE if X consists of several pieces
  which are not joined together.
  
The function is.connected is generic.
  The default method is.connected.default 
  works for many classes of objects, including windows (class "owin")
  and images (class "im").
  There is a method for linear networks, is.connected.linnet,
  described here, and a method for point patterns
  described in is.connected.ppp.