Stitching is a method of taking multiple photographs that overlap and putting them together to get a much larger photo. For landscapes and cityscapes especially, it can make for a much larger more detailed photo in a large print. You can effectively end up with a photo that would require the equivalent of a 100 megapixel camera or more (not to mention the lens!) Stitching is commonly used for long panoramic photos.
Putting a bunch of photographs together at first glance looks pretty easy. Many digital cameras include some sort of stitching software in all that junk on the CD you probably stuffed in a drawer somewhere. I loaded mine on my computer, "Canon PhotoStitch". However, if you look close a the photos below, you can begin to see problems where the seams of the neighboring photos are.
The first photo, a string of 14 photos shot left to right (16,000+ pixels wide once stitched) had two main problems, the first of which doesn't show up here. Because I was shooting "handheld" I didn't stay exactly level, I ended up having to cut parts of the bottom of the photos on the left off that I really would have liked to keep, and parts of the top off of the photos on the right. Use a tripod next time, and if necessary, do two rows. The other problem shows up especially in the roof of the house on the right. The exposure changes as I move across the scene. So next time, I'll take a shot of the brightest part of the scene and a shot of the darkest part of the scene and then in manual setting, use a constant aperture (which I already remembered to do) and a constant shutter speed (which I this time I let vary with each exposure) that will "work" with both the brightest and the darkest portions
The second photo (a vertical stitch of 3 photos) has some problems too. The varying exposure again, the distortion that comes from using a very wide angle lens, and I didn't leave enough overlap between the bottom photo and the middle photo, so I had to "help" the software a little more than should have been necessary. Next time, don't use such a wide angle, just take more photos instead, and make sure to overlap enough details for the stitching software to work with.
Last, getting a good stitch is probably the easy part. Afterwards, the finishing work (which I didn't do at all on these photos) such getting the colors, sharpness, relative brightness etc all right could be tremendously time consuming and tedious across a huge 16000+ pixel photograph. And very last, at least the way I have the blog set up now, 1024 pixels is as wide as things can go, so you really don't see much once I reduce a photo to 1/16 the original size.