The long line is called the strike line, and shows the direction in the bed that is still horizontal. The strike line shows that horizontal direction in the beds. The short line is called the dip line, and shows which way the bed is tilted. The number is called the dip, and shows how much the bed is tilted, in degrees, from flat. The higher the number, the steeper the tilting of the bed, all the way up to 90 degrees if the bed is tilted all the way onto its side.
All geologic maps come with a table called a map key.
In the map key, all the colors and symbols are shown and explained. After the list of geologic units, all the different types of lines on the map are explained, and then all the different strike and dip symbols. Because the geology in every area is different, the map key is vital to understanding the geologic map. The geology of an area has a profound effect on many things, from the likelihood of landslides, to the availability of groundwater in wells, from the amount of shaking suffered in an earthquake, to the presence of desirable minerals, from the way the landscape is shaped to the kinds of plants that grow best there. Understanding the earth underneath is the first step in understanding the world around us.