Deltiology is the name for the study of postcards. If you decide to collect postcards for a hobby, you might choose to collect only those with ice skaters on the front. Or, maybe you'll choose teddy bears, flowers, mountains or dogs. Some collectors pick only photos of buildings, trains or elephants. There are thousands of choices.
Some people get into collecting in a big way with over a million cards in their collection.
Cards with pictures of places on them are popular, too. Vacation places like the Grand Canyon, Disneyland and Yellowstone Park are fun to collect. Most big parks, restaurants and hotels have postcards with their photos on them. A book store or card store near your house probably has postcards of your town. They might show buildings, lakes or parks that you have visited.