North America spreading out into nothingness

Earlier today, I was talking to a woman that I work with about ancient maps. We were joking about how odd some of them looked compared to actual pictures of the planet. I always found it interesting that, on many early maps, the detail of certain places was so precise while others were just way off. I am impressed by how accurate some of these mapmakers were with Europe and Africa in particular. Sometimes with only accounts from explorers, merchants, etc., these mapmakers would create nearly exact representations of islands, countries, and continents.

One of the more odd representations that I've seen is shown below. In it, Europe, Africa, and Asia seem to be pretty spot on. But North America is this odd blobby thing that kinda fades off the edge of the map. I figured that this was so because people didn't know much about North America at this point, but the map was made between 1749 and 1784. While much of the extent of North America was not known until Lewis and Clark (and others) returned in 1806, surely there was as much knowledge about North America as there was about Africa at the same time. I wonder why the map doesn't reflect this. Maybe I'm missing something obvious, but it seems to me that if they could (fairly) accurately reflect the size and shape of Africa, Asia, and South America, they could do it with North America as well.



[Click on the map for a larger image]