Okay kiddo, do you know what a map is? It's like a picture that shows you where different places are.
Well, a chart is a type of map but it's for the water instead of the land. It shows sailors where they are in the sea, and what obstacles or dangers might be nearby.
The Thames School of Chartmakers was a group of people who made lots of these charts for sailors to use along the River Thames in London, England. They started doing this many years ago, back when ships were the main way of traveling and trading goods.
These chartmakers were very important because they helped sailors navigate safely through the Thames River and avoid running into things like rocks or sandbars. They used a lot of different tools like compasses, rulers, and even special math formulas to make sure their charts were accurate.
So, the Thames School of Chartmakers was a group of people who made maps for sailors to use on the river, and they were really good at it!