A map consists of one or several layers, each of which contains one or several feature types. Each type has a set of features which belong to it.
Map layers and feature types are map components, and the map itself is one of GDB components.
Map partition into layers and feature types fully depends on the wishes of the user who creates a map. It usually reflects actual feature interconnections and depends on the map's purpose. Features which have equal set of describing characteristics usually belong to one type. For example, all buildings have such characteristics as the number of tenants, the number of storeys, the year of repairs, etc. All parcels have different characteristics – type of ground, parcel's purpose and so on. In this connection it would be reasonable enough to consider buildings and parcels as different feature types.
When performing map partition into layers, it is necessary to take into account that map displaying is carried out layer by layer and the user can specify the required order of layers (from the lower to the higher). Features of the layer which is displayed later (the higher layer) can overlap features from the layers displayed earlier (lower layers). In contrast with it, for feature types of one layer a definite displaying order is not guaranteed.
It is always possible to change the current partition into components, introduce new layers or on the contrary, merge the current ones, change the layer or the type for some features and so on.
To create a new map, one should put its name into the map list of the particular GDB, describe the map layers and feature types in each layer using ObjectLand tools. Right after creating a map, it is empty, that is, it doesn't contain any features.
ObjectLand provides means for adding, changing and removing features (map editing). Features can also be added to a map as a result of import operation, that is, loading of a file with feature description set in one of the formats supported by ObjectLand. Import procedures will be described in a separate section. Besides, features may be transferred from another map as a result of an operation of merging maps or their components.
Demo GDB “City” contains maps “N-City” and “N-City region”. Below, when describing map structure, examples based on these maps will be shown.
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