Imagine a scenario where we want to show all the gas stations in every city around the world. What will happen when the user navigates within the map and sets a zoom level to look at the whole world? We're presented with an overwhelming dominance of points, overlapping each other all at the same place, providing little visual value to the user.
A solution to this problem is to cluster the features on each zoom level. OpenLayers makes this very easy to implement.
This recipe (source code in
ch03/ch03-clustering) shows how easy it is to apply clustering on a vector layer, which is responsible for grouping the features to avoid a situation similar to the one discussed earlier that can be seen in the following screenshot: