The OpenLayers
format is a special case. Indeed, when you ask for it, GeoServer is not answering with a single object, but with a full web application. As you learned, the application then issues other WMS requests to get a representation of the map.
In the following sections, we will discover what formats you can use and which are best suited for your applications.
The Atom Publishing Protocol (AtomPub) format is a XML-based output. Also known as a Vector output type, it is comparable to RSS feeds, which are more common. It allows others to subscribe to features published by GeoServer. The output format is specified by application/atom+xml
as the format parameter value.