In Canada, there is a very strict way to make areas dark-sky preserves. This was based on the work by the Royal Astronomical Society of Canada. The program is based on the amount of light in an area and how much skyglow there is from cities and towns that are close to it. Canada's program is the only one in the world that makes areas dark-sky preserves. Outside Canada, when areas are called dark-sky preserves, they are not official, and might not be a real dark or protected preserve.