This chapter is all about working with raster layers. We have tried to summarize, with a set of recipes, the most common and important use cases you can find day-to-day when working with OpenLayers.

Imagery is one of the most important kinds of data to work with in a GIS system.

OpenLayers offers several classes to integrate with different imagery providers, from proprietary providers such as Google Maps and Bing Maps, to Open Source ones such as OpenStreetMap or even any WMS service provider.

The base class for any layer type is the OpenLayers.Layer class, which offers a set of common properties and defines the common behavior for any other classes.

In addition, many layers inherit from the OpenLayers.Layer.Grid class, which divides the layer into zoom levels. This way each zoom level covers the same area but uses a greater set of tiles. For example, at level zero a grid with one tile covers the whole world, at level one a grid with four tiles covers the whole world, and so on. As we can see, on each level, the number of tiles and their resolution increases.

This chapter introduces you to the use of raster layers, with special attention to the WMS layers, and how to manage the most common properties.