It might not make much sense at first. "Why try to keep in touch with someone if you'll only see them once a year or once in a lifetime? Why waste all this time and effort?"
Well, friends aren't easy to come by. Most people you meet will either fall into one of two categories: acquaintances or friends. However, when you have a special connection with someone, you want to keep that for as long as you possibly can. Thus, you make the effort to keep in touch with them and get to know them better. And when two people who are genuinely interested in each other's well-being create a friendship, it is priceless.
Your communication will mainly consist of messaging apps and pictures, tagging them in countless Instagram posts, and possible weekly phone calls (when time zones allow for it). With messages, pictures, and phone calls, you won't notice the distance as much and you'll feel that you're a part of their life, and they're part of yours.
Eventually, you'll make plans to meet up with them and do stuff together during your time in their province/country (or vice versa). You'll wait anxiously for the day to come when you see them, and when you do see them - it'll be filled with excitement and bliss. You'll cherish your time with them because you won't be able to see them again until the next scheduled meet-up. Be sure to take photos with them - you'll have memories to cherish. It'll also help you in those moments when your heart aches for them.
Is it hard to maintain a long-distance friendship? Yes, definitely.
But is it worth it? Absolutely, 100%.