RailNetworkSegments, have both a GDF1 and GDF2 representation. A GDF1 is required for all railways. GDF2 is required for Standard (mainline) railways only. RailNetworkSegments, have both a GDF1 and GDF2 representation. A GDF1 is required for all railways. GDF2 is required for Standard (mainline) railways only. Following European standards, a Network is derived from centreline data. A Network consists of a set of specified points, linked together by lines. The GDF1 represents the centreline of the railway. The GDF2 is the same as the GDF1 except that in an area where there are two or more lines travelling in parallel a single GDF2 line is used to represent all the parallel lines. This is very useful in the approaches to rail stations, where there may be a considerable number of such lines. PRIME2 does not represent the actual real world metal rail tracks. This means that the RailNetworkSegment does more work than other NetworkSegments - although the lines and points are notional, they carry full responsibility for representing the railway.