<br>where type1 defines this as a link record type and label serves as an identifier to distinguish this link from all others. the z1 and z2 fields determine the vertical separation of this link from others sharing the corresponding nodes node1 and node2. thus an overpass to a link, for example, can be represented as not connected to that link. other record types are used to represent address information, shape-points for a link, cities and states, points of interest (poi's), etc.