Web Map Service (WMS) is an OGC standard for serving up map images over HTTP. Map images are usually generated by a map server using data from GIS database. This format is similar to map tiles, but more general and not so well optimized for using in web applications.
WMS supports a number of different request types, but the main operations are:
GetCapabilities — an operation that returns an XML document describing the service (supported parameters, image formats, available layers, etc.).
GetMap — an operation that returns a map image for a specified area and content. The add-on uses this operation to obtain images from WMS.
It’s important not to confuse the concept of the add-on’s layer with the layer in WMS. WMS provides a set of layers defined in the
GetCapabilities XML document. The WMS Layer of the add-on displays the resulting images provided by WMS. These images are being built using one or more layers in WMS.
The add-on does not work with GetCapabilities operation, so you can find out the information about the available layers in WMS in one of the following ways:
XYZ is a de facto OpenStreetMap standard, also known as Slippy Map Tilenames, defining scheme for tiles that are served through a web server.
These tiles can be accessed via URL following certain pattern:
z is the zoom level, and
y identify the tile.
For example, OpenStreetMap tiles URL pattern is:
Tile servers based on OpenStreetMap data.
Tile providers preview — here you can find and preview various XYZ tile services. Some of them are free, while others require registration and may have free tile requests limit. Be sure to check the providers usage policies before using them.
Mapbox tile API.
HERE tile API.