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.