Throught the whole "on the road again" song, there is clear representation of journey, as they walk from the cave "thats the moon donkey" to the final place of "weed-rat". Thats all physical journey. And the song is a technique (and a related text in itself).
This is my little set up of the movie. Its not very good at all though. Just quick to satisfy to my teacher that I do work.
The purpose of Shrek’s journey is to give the beautiful Princess Fiona to Lord Farquad, and also to get the deed of his swamp back. Shrek’s catalyst for this journey are meeting Donkey, and Donkey’s behaviour as to what he calls friendship. Another matter crucial for causing Shrek’s journey is the placement of the “fairy-tale creatures” in his swamp, and his desire to be rid of them. The dialogue in this opening introduction is, from Shrek, an exasperated tone, which adds to the fact that he prefers his own company.
On the journey he learns very important things about himself. He falls in love with Fiona, learning that beauty is on the inside, not the outside, and that love is stronger then looks. that he could always use a friend, and how important friendship is. He finds a new respect for himself and others, and learns of the nature of the world, and that it is not as ‘anti-ogre’ or ‘racist’ as he thinks. He learns that there is some good in the world, and not everyone is against him.
There are many things which Shrek has to overcome, both physically and mentally. These include the Dragon, who he has to defeat to get Fiona to return to Lord Farquad, who he then has to overcome aswell, as Lord Farquad is a very ‘racist’ person, instantly taking a dislike to Shrek because he is not a human. Donkey and Fiona are more complicated, as he instantly takes a grudge against them for his attitude to them both being ‘racist’. He slowly sees that the world is not as cruel as he thinks, and begins to show his feelings, though as soon as he does, he loses faith in everyone but himself again when he assumes that everyone this he is ugly. At last, the final challenge he has to overcome is his self-perceived ugliness.
Finally, Shrek gets Fiona, because of his personality and innocence, not his looks. He looks past himself and sees what’s inside of him, begins to open up to people instead of following his recluse behaviour. His attitude to people and society in general has changed now, as he feels more accepted into average life. (though not for long, right “Shrek 2?”)
Like I said, it's not great, but its a start.