There are two kinds of layers in ObjectLand.
Layers of map, layers of EDB and work layers of theme contain graphic features and differ only in their place in the hierarchy of GBD components.
Layers of theme based on map layers do not themselves contain any features and are rather references to map layers. At that, such a layer of a theme can include not all features of a map layer but only part of them, taking into consideration actions of filters and scale zones.
A layer of any kind can serve as source of copying, however a layer of theme based on a map's layer can not be destination of copying. Thus, possible destination layers for operations of copying, moving and merging layers include the following:
a map layer;
an EDB layer;
a work layer of a theme.
Further, map layers will be considered for short, but all this information is also valid for layers of theme and layers of EDB, unless contrary is not mentioned.
When performing the operation of copying a layer, a destination layer containing a copy of the source layer is created in the destination map. A copy can be incomplete: it is possible to omit all features of a certain type or specify some rectangular region of copying. Apart from the source layer itself, other GDB components which are linked with the layer some way or other take part in the operation: tables linked with types of the source layer; library styles of source GDB used in the layer.
The operation of moving a layer consists of two stages: copying the source layer to the destination map and removing the source layer from the source map. The source layer is removed with all features and links between features and table records not depending on whether the region of copying has been specified or not. Removing of the source layer does not cause removing of tables linked with the source layer; records of these tables; queries built on the basis of these tables; library styles of source GDB used in the source layer.
Merging of layers differs from copying firstly in the fact that the destination layer already exists. Feature types of the source layer are added to the destination layer as new types or they are merged with the existing types of the destination layer. In the last case feature types being merged should have the same spatial category. Links between types being merged and tables can be different. Merging types is understood as copying of features of the source layer belonging to the present type to the destination layer. The corresponding type of the destination layer will be set for copied features.
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