William Smith (geologist)
In 1799 Smith produced the first large scale geologic map of the area around Bath, Somerset. Before, he only knew how to draw the vertical extent of the rocks, but not how to display them horizontally. Then, in the Somerset County Agricultural Society, he found a map showing the types of soil and vegetation around Bath and their geographical extent. The different types were coloured. Using this technique, Smith could draw a geological map from his observations showing the outcrops of the rocks. He took a few rock types, each with its own colour. Then he estimated the boundaries of each of the outcrops of rock, filled them in with colour and ended up with a crude geological map.