Franklin does all the hard work, I just do the proof reading and occasional site visit
Believe it or not, a lot of information gathering it is hard slog viewing Google Earth and following every bit of track and pointwork. That does have its problems as many of the recent GE views are rubbish (unkess you like dark clouds!) and so an earlier, clearer, historical view often has to be used as the layout basis to start with and then checked for current layout later.
Network Rail publish various sources online such as:
Rules of the plan (Timetable planning rules) for each area
Sectional Appendices for each area
which give detailed track layouts, junction names etc.
The layouts are not to scale and there is a lot of hopping from one part of a line to another if following a certain route etc. and, unless the pages printed off, can be hard to follow sometimes.
The problem with these is that they are not error free and layouts are not always shown correctly or some parts may be omitted. Likewise junction names can vary between publication, even though they are for the same location!
Large scale Ordnance Survey maps are another useful source of layout and naming information. Alan Godfrey Maps have been reprinting 1:2500 scale OS maps. They started with London first and gradually extended to other main areas (see their site). Their maps cover from the first series (1860s) to the fourth series (1930s) and it depends on the area as to what series are available. These are the maps that many libraries have for sale in the local history section. They can also be bought at other places, such as Foyles etc., but they are usually more expensive than if bought direct from Alan Godfrey, especially if you want several as a reasonable P&p charge covers whatever amount is ordered.
I have all of the maps that he has printed for the GLC area and many beyond that. There may be a map of each series (4 in all) for many of the central area. I find them very useful, and it is also fascinating to see how things have changed over the years, especially if there maps for each series to compare the area with.
Maps at this scale show a wealth of information as far as the railways are concerned, often including every signal post. The track layouts are very detailed and, depending on the map series, junctions may be named and the position of underground tunnels shown.
Obviously track layout changes over the years, although most of the changes involve the track being lifted and built over and there is sometimes very little change to the main running line layout.
Then, of course, there's always Google if searching for anything specific like a signal diagram / track layout or junction name (although many junction names have changed several times over the past 150 years).
Getting information is usually a mixture of the things mentioned and, where necessary, a site or line visit to check the layout. This happened with the LO NLL as the latest GE available at the time showed the original NL track or sections of lifted track where the new layout was being installed. E.g. the 2010 GE view of Canonbury was the nearest clear view of the area at the time and that just shows lots of bare track bed, ballast wagons and cranes!
