Ian McHarg was a man who really enjoyed maps and nature. He wanted to make sure that people took care of the environment so that it didn't get all messed up. So, he figured out a way to make maps that showed how humans could use the environment without hurting it too much.
For example, he would make a map of a city and show where all the people lived, where the stores and buildings were, and where the rivers and mountains were. Then, he would add a layer to the map that showed how animals like birds and fish used the environment. He would also show which areas were good for farming, which were good for building homes, and which were important to keep natural for everyone to enjoy.
By making these special maps, Ian McHarg helped people make better decisions about how to use the environment. He wanted to make sure that we could still enjoy and use the land, but without hurting it too much. And that's what he did.