Friday, January 29, 2010
Google
Layer for using Google Maps data within OpenLayers. For API information, see the Google Layer API Docs. For an example of usage, see the Spherical Mercator example.If you are overlaying other data on a Google Maps base layer, you will want to be interacting with the Google Maps layer in projected coordinates. (This is important if you are working with imagery data especially.) You can read more about the ‘Spherical Mercator’ projection that Google Maps – and other commercial layers – use in the Spherical Mercator documentation.
The Google Layer class is designed to be used only as a base layer.
Raster Layers
Non Base Layers
Non Base Layers
Non base layers – sometimes called overlays – are the alternative to Base Layers. Multiple non-base layer can be enabled at a time. These layers do not control the zoom levels of the map, but can be enabled or disabled at certain scales by min/max scale/resolution parameters so that they are only enabled at a certain level.Some types of overlays support reprojection to the base layer projection at layer load time. Most overlay layers default to non-base overlays, as does the base Layer class. Non-base Layers always display above base layers.
Base Layers
Base Layers
Base Layers are mutually exclusive layers, meaning only one can be enabled at any given time. The currently active base layer determines the available projection (coordinate system) and zoom levels available on the map.Whether a layer is a base layer or not is determined by the isBaseLayer property on the layer. Most raster layers have the isBaseLayer property set to true by default. It can be changed in the layer options.
Base Layers always display below overlay layers.