Bridging the geometry of two parts of an object that were created separately I am creating a chair and I created the backrest and the seat portion separately. I joined them and I want to model the transition between them but I don't know how to go about it

Here's the chair I'm referencing:



Link to my blender file:

https://drive.google.com/open?id=0BxtZBZThYAyjaHVjUEk2TFAxcFk

Thank you!
@LukeD is right.
You could in edit mode use select edge loop and dissolve edges(ctrl X) to decrease the number of edges of the armchair. Subdivide the lower edged parts to get more edges to work on. Try to conect these vertices now.