Yesterday, Amy was asking if there was a library for drawing curved lines between two points on a map. She wants to use this for her travel posts, which say for example "Tokyo to Boston". We noticed that Facebook draws curved lines when they show a planned trip. Martijn was able to figure out how to reproduce this on Facebook consistently. You have to start by creating a "checkin" post, then add a "traveling to" activity to it. Notice that the line from Portland to Seattle is curved rather than straight, although it doesn't strictly follow a Great Circle line either.