Tilt shift photography is an effect traditionally achieved using small to medium format cameras and special lenses. The resulting photograph gives the impression that a life sized subject or location looks like a miniature model. I am going to show you how to quickly (depending on your processor speed) achieve this effect by using Photoshop.
First, you will need a photo taken from a good vantage point. Choose something taken from a high altitude or from afar. I took this one whilst walking along the Thames in London:
Now open your image in Photoshop and click the Quick Mask button located at the bottom of the tool bar (see image on the right).
Select the gradient tool and apply it onto the quick mask layer so that the areas you wish to be out of focus are red. See the screen shot below:
Now click the quick mask button once again, and go to Filter > Blur > Lens Blur. You will see dialog below:
You can then simply play with the Radius and other sliders to simulate your desired ‘depth of field’. Check out my final tilt shifted photo here. Have fun 
I’ve tried this technique before and it just doesn’t feel right to me. I shot medium format and large format for years starting back in college and the photoshop versions feel less smooth and dare I say it, randomized. It’s probably just nostalgia on my part but there has got to be a better way to do this in photoshop. If you think of anything please enlighten me!
http://irenejonesphoto365.blogspot.com