A label layer contains the definition of labels based on the features in one or more tables. Each label layer contains one or more label sources which are either included in the label layer (inline) or referenced as a separate named resource (named label source). For more information, see Named Label Sources in the Resources and Data section.
Labels typically contain the value of column, but can also contain derived information as the result of an expression.
Each label source controls the visibility, base label properties, and themes applied to a particular set of labels. The sets of labels for a map is derived by determining the labels for each label source in order from top to bottom. This means that the first label source has the highest priority and other labels trying to be placed in the same location may not appear, assuming that overlap detection is enabled.
Label properties determine the visibility, style, placement, and priority of the labels. Themes control how the label properties are applied:
A label layer that is used as an entry in a named map can be used by a Render Named Map request. A label layer that is used as an entry in an inline map can be used by a Render Map request. In both cases the label layer can be inline or a named layer resource of its own that is referenced by the map just like other named layers. A label layer can also be used as an item in a group layer.