+ # These are hastables that store an id in the index of all
+ # the nodes/way/relations that have already been added.
+ # Once we know the id of the node/way/relation exists
+ # we check to see if it is already existing in the hashtable
+ # if it does, then we return false. Otherwise
+ # we add it to the relevant hash table, with the value true..
+ # Thus if you have nodes with the ids of 50 and 1 already in the
+ # relation, then the hash table nodes would contain:
+ # => {50=>true, 1=>true}
+ nodes = Hash.new
+ ways = Hash.new
+ relations = Hash.new