Developer's Guide - MapGuide Open Source - OSGeo

Overview of Layers
Layers represent vector data, raster data, and drawing data in a map. Each type
of layer has unique characteristics.
NOTE The word layer has different meanings in different contexts. A layer can
refer to the layer definition in the resource repository, and it can also refer to the
map layer. For the purposes of the Web Tier, a layer refers to a map layer, and a
layer definition refers to the layer definition in the resource repository.
Basic Layer Properties
Layer Groups
A map contains one or more layers (MgLayer objects) that are rendered to
create a composite image. Each layer has properties that determine how it
displays in the map and map legend. Some of the properties are:
■ Layer name: A unique identifier
■ Legend label: The label for the layer as it appears in the map legend.
■ Visibility: whether the layer should be displayed in the map. Note that
actual visibility is dependent on more than just the visibility setting for a
layer. See Layer Visibility (page 26) for further details.
■ Selectable: Whether features in the layer are selectable. This only applies
to layers containing feature data.
The MgMap::GetLayers() method returns an MgLayerCollection object that
contains all the layers in the map. The MgLayerCollection::GetItem() method
returns an individual MgLayer object, by either index number in the collection
or layer name.
Layers in the collection are sorted by drawing order, with the top layers at the
beginning of the collection. For example, using PHP syntax, if $layers is a
collection containing the layers in a map, then $layers->GetItem(0) returns
the top-most layer.
Layers can be optionally grouped into layer groups. Layers in the same group
are displayed together in the legend.
24 | Chapter 2 Interacting With Layers