The BBC has put together a cool website that maps certain physical features, manmade features, or events onto other maps to provide a sense of scale.
Once we get to large numbers, many of us are not very good with visualizing how large something is. Take, for example, the national debt – it is nearly beyond comprehension. Or the distance between Earth and the sun. Or the population of China. We tend to think in smaller units so larger numbers tend to cause problems. People who operate in such units try to break it down into more manageable sizes: this is the average debt per US citizen, that distance would equal X number of trips from the Earth to the moon, that population would be roughly 37 times the population of California.