Defining custom rules to style features

We will see a brief explanation before continuing with this recipe. The goal, as in the other recipes in the chapter, is to style the features of a vector layer depending on their attributes' values or their kind of feature.

So, an OpenLayers.Layer.Vector layer class can have an OpenLayers.StyleMap instance associated with it, which determines the default style of the layers if it has only one OpenLayers.Style, or the set of styles that can be applied for each render intent if it contains more than one OpenLayers.Style. In its own way, each OpenLayers.Style instance can be used in two forms:

• Having a symbolizer hash acting as the default style to apply to the features

• Having some OpenLayers.Rule instances associated with it

Here we arrive to the main concept of this recipe, the rules.

A rule is nothing more than a join between a filter (concretely an OpenLayers.Filter) and a symbolizer, if the filter matches the feature then the symbolizer is applied...