The map on the right could be your city, or your county/state/province or maybe even your country depending upon population density
So, this is how it works. I will use the sending of an email plus attachments as an example.
Your email is constructed in your preferred email client and looks to be in one complete piece, but before it can be sent anywhere, it is broken down into tiny little pieces, each of which contains sender and recipient information plus some data, part of the text or photos.
Each piece is sent on its way and, on a good day, the pieces will follow each other across the shortest route. If one of the routers on the shortest route starts to fail or just collapses, some or all of the pieces will be diverted.
If the pieces have then to pass through one of the routers working at reduced capacity, some may not get through and be diverted again. This process continues until all of the pieces meet up again at the recipient's ISP or local web based mail server. Then and only then will you get the 'You got mail' message.
If you are a vehicle driver, you will know all about hold-ups at rush hour, and your e-mail can experience the same problems. As distance to the recipient increases, so does the chance of it being held up.