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. these are usually formed by a closed polygon, which are shapes that indicated an object over a map has to have a close boundary, meaning the first polygon should be same as a last polygon. (for example, to plot a square object on a map, the polygons are 1,2,3,4,1.)