Content of A Map Database
A map database represents a road network along with associated features. Map providers choose various models of a road network as a basis to formulate a database. Commonly, such a model comprises basic elements (nodes, links and areas) of the road network and properties of those elements (location coordinates, shape, addresses, road class, speed range, etc.). The basic elements are referred to as features and the properties as attributes. Other information associated with the road network is also included, including points of interest, building shapes, and political boundaries. This is shown schematically in the image to the right. Geographic Data Files (GDF) is a standardized description of such a model.
Each node represents a point location of the surface of the Earth and is represented by a pair of longitude (lon) and latitude (lat) coordinates. Each link represents a stretch of road between two nodes, and is represented by a line segment (corresponding to a straight section of road) or a curve having a shape that is generally described by intermediate points (called shape points) along the link. However, curves may also be represented by a combination of centroid (point or node), with a radius, and polar coordinates to define the boundaries of the curve. Shape points are represented by lon, lat coordinates as are nodes, but shape points do not serve the purpose of connecting links, as do nodes. Areas are two-dimensional shapes that represent things like parks, cities, blocks and are defined by their boundaries (usually formed by a closed polygon).
Read more about this topic: Map Database Management
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