Map database management

Map database management systems are software programs designed to efficiently store and recall spatial information. They are widely used in localization and navigation, especially in automotive applications. Moreover, they are playing an increasingly important role in the emerging areas of Location-based services, Active safety functions and Advanced Driver Assistance Systems. Common to these functions is the requirement for an on-board map database that contains information describing the road network.

When designed well, a map database enables the rapid indexing and lookup of a large amount of geographic data.

Maps are stored as graphs, or two dimensional arrays of objects with attributes of location and category, where some common categories include parks, roads, cities, and the like.

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 adjacent image. Geographic Data Files (GDF) is a standardized description of such a model.

Each node within a map graph 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).

Closed polygon: a polygon or a shape file that indicated an object over a map, has to have a close boundary, meaning your first polygon should be same as a last polygon.

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