Kindle, although being a really good e-reader has received a bad rap because of not having page numbers. Amazon is adding real page numbers for books gradually, but 'Locations' are the primary means of telling the progress in a book and synchronizing with other devices.
But Amazon does not explain what these Locations are. While no one seems to be really sure how big a Location is, we certainly know what they are, why they are and how they work. This article explains it all.
We know quite a lot about it. Even how big they are. Read on to find out.
Locations in the Kindle ecosystem (the devices and the apps for Windows, Mac and mobile platforms) are basically a way to keep track of your reading progress in a book, kind of like real page numbers. However, page numbers won't necessarily work. The Kindle ecosystem spans across several different platforms running on different devices. The screen sizes are all different. Moreover, you can change the size of the text also. If you read a Kindle book on your iPad and then continue reading it on your iPhone, the screen size will not be consistent and not the same amount of words will fit onto the devices.
To sync progress in a book in this confusion, Amazon uses Locations. A Kindle book is divided into tiny bits. Every few lines, a new Location begins. Your Kindle (or an app) remembers the Location on top of the screen every time you turn a page. When you switch to another device, the Location that was on top of the screen of your first device will appear on the top of the screen of your other device.
That's why, if you read just a few paragraphs on your iPhone (which was less than the text on one screen of your iPad), and switch back, the Kindle app on your iPad will sync and move some text that was in the middle of the screen to the top. Thus, the Location on top of the screen stays consistent. This is the reason Kindles and Kindle apps seem to shuffle a few lines here and there when syncing and then turning pages.
EDIT: Several people on the Internet say that each Location is 128 bytes of text.
See also: Beginners' Guide to jailbreaking an Amazon Kindle.