Darkoshi

In some U.S. states, the highway exits are numbered sequentially. If you've just passed exit 7, you know that the next exit is #8, but you don't know how far away it is.

But in other states, the highway exits are numbered based on the mile-markers. At the start of the highway, or where-ever the highway enters the state, the mile-markers start at number one. Each exit is numbered based on the nearest mile-marker. So if you've just passed exit 7, you know that you're about 7 miles from the start of the highway, and you can tell that exit 18 (for example) is about 11 miles away. Or if you've just passed mile-marker 12, you know that exit 18 is about 6 miles away. If you look at the map and see that the last exit is #49 (for example), you can tell that the highway was 49 miles long.

I didn't know this. It is useful!