Abstract Base Classes for Map Databases

vhclmaps contains a set of C++ classes for representing map databases (the Map library). The base classes are an abstraction of the structure of the Vector Product Format (VPF) that was used for the Digital Chart of the World (DCW). One set of derived classes was written to handle VPF, another for DLG (Digital Line Graph from the USGS). The abstract base classes in this library are:

• MapDatabase: represents an entire data collection, usually originating from a single geodata product. Examples: DCW, DLG 1:2M.
• MapLibrary: represents divisions of a database by geographic extent. Examples: DCW noamer (North America), DLG 1:2M sect01 (Northeastern States).
• MapCoverage: represents thematic layers of general map feature categories. Examples: Political/Oceans, Roads, Water Bodies.
• MapFeatureClass: represents the different geometric types of map features. Examples: Area Features, Line Features, Point Features.
• MapFeature: represents individual geodata elements. Examples: individual roads, lakes, rivers, islands.

This diagram illustrates the structure of a map database and the layers of the framework:

Individual map features are contained within a hierarchically structured set of collections. The collection at each level contains objects selected according to the various classification criteria: geometric shape, thematic type, and geographic location. Each collection provides methods to access its list of objects. Derived classes implement format-specific methods that obtain raw data to construct object instances.

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