Maps can contain an overwhelming amount of information, but some maps don't show enough. Figuring out just what information to display on a map is certainly an art form, and creating printed maps with just the right balance of information is quite difficult.

Fortunately, creating maps for the web is slightly easier in this respect, because we can let the user determine what information they want to see. Imagine two people looking at a city map—one person just cares about the bus routes, while the other wants to only know about bicycle routes. Instead of creating two maps, we could create a single map with two different layers, one for each route. Then the user can decide if they want to see the bus routes, bicycle routes, both, or none at all.

OpenLayers provides us with a variety of layer types to choose from and use. We can do all sorts of things—such as changing layer opacity, turning the layers on or off, changing the layer order, and much more.