Amazon is one of the only things keeping the US Postal service afloat

The US Postal Service does a staggering amount of work, when you sit down and really think about it: it delivers 158 billion pieces of mail per year, the vast majority of them on time. And it also has some staggering financial problems.

All of those troubles have a lot to do with digital communications -- it's quicker to send Grandma an e-mail or even a text than a card -- but there are plenty of other moving parts. Here are 9 charts that explain what's going on with the US Postal Service.

1. The westward spread of postal service
2. The fast death of your friendly neighborhood mailman
3. The check is not in the mail
4. Lots of work for far fewer workers
5. The ever-rising (but really quite stable) cost of postage
6. Revenues vs. expenses
7. Packages are helping the USPS stay afloat
8. Prefunding retirements
9. Postal banking