@Kupod5uR
As I’ve written software for both LOROL and Arriva Rail London, which did use a list of internal ids to group the lines as I described about, there is no public interface that has these.
This is what they used
Line names and IDs
"1","Watford Junction to Euston","DC"
"2","Richmond to Stratford & Willesden Junction to Clapham Junction","NWLL"
"3","Gospel Oak to Barking","GOB",
"4","Highbury & Islington to West Croydon/Clapham Junction","ELL",
"5","Liverpool Street to Edmonton Green, Enfield Town, Cheshunt & Chingford","West Anglia"
"6","Romford to Upminster","RU",
This is broken down into sub-lines (subline ID, line ID, name)
(1000, 1, 'Watford Jct DC'),
(1001, 2, 'Rchmnd-Strtfrd'),
(1002, 2, 'Wllsdn-Clphm J'),
(1003, 3, 'Gpl Oak-Brkng'),
(1005, 5, 'Enfield T WA'),
(1006, 5, 'Chingford WA'),
(1007, 5, 'Cheshunt WA'),
(1008, 6, 'Rmfrd-Upmnstr'),
(4001, 4, 'New Cross ELL'),
(4002, 4, 'Clphm Jct ELL'),
(4003, 4, 'W Croydon ELL'),
(4004, 4, 'Crystal Pal ELL'),
(9999, 4, 'ELL Core');
So that puts stations in sublines like this … -1 means “served by more than one sub-line”
"Acton Central","1001","ACC"
"Anerley","4003","ANZ"
"Barking","1003","BKG"
"Bethnal Green","-1","BET"
"Blackhorse Road","1003","BHO"
"Brockley","-1","BCY"
"Brondesbury","1001","BSY"
"Brondesbury Park","1001","BSP"
"Bruce Grove","-1","BCV"
"Bush Hill Park","1005","BHK"
"Bushey","1000","BSH"
"Caledonian Road and Barnsbury","1001","CIR"
"Cambridge Heath","-1","CBH"
"Camden Road","1001","CMD"
"Canada Water","-1","ZCW"
"Canonbury","-1","CNN"
"Carpenders Park","1000","CPK"
"Cheshunt","1007","CHN"
"Chingford","1006","CHI"
"Clapham High Street","4002","CLP"
"Clapham Junction","-1","CLJ"
"Clapton","1006","CPT"
"Crouch Hill","1003","CRH"
"Crystal Palace","4004","CYP"
"Dalston Junction","-1","DLJ"
"Dalston Kingsland","1001","DLK"
"Denmark Hill","4002","DMK"
"Edmonton Green","-1","EDR"
"Emerson Park","1008","EMP"
"Enfield Town","1005","ENF"
"Euston","1000","EUS"
"Finchley Road and Frognal","1001","FNY"
"Forest Hill","-1","FOH"
"Gospel Oak","-1","GPO"
"Gunnersbury","1001","GUN"
"Hackney Central","1001","HKC"
"Hackney Downs","-1","HAC"
"Hackney Wick","1001","HKW"
"Haggerston","-1","HGG"
"Hampstead Heath","1001","HDH"
"Harlesden","1000","HDN"
"Harringay Green Lanes","1003","HRY"
"Harrow And Wealdstone","1000","HRW"
"Hatch End","1000","HTE"
"Headstone Lane","1000","HDL"
"Highams Park","1006","HIP"
"Highbury And Islington","-1","HHY"
"Homerton","1001","HMN"
"Honor Oak Park","-1","HPA"
"Hoxton","-1","HOX"
"Imperial Wharf","1002","IMW"
"Kensal Green","1000","KNL"
"Kensal Rise","1001","KNR"
"Kensington (Olympia)","1002","KPA"
"Kentish Town West","1001","KTW"
"Kenton","1000","KNT"
"Kew Gardens","1001","KWG"
"Kilburn High Road","1000","KBN"
"Leyton Midland Road","1003","LEM"
"Leytonstone High Road","1003","LER"
"Liverpool Street","-1","LST"
"London Fields","-1","LOF"
"New Cross","4001","NWX"
"New Cross Gate","4003","NXG"
"North Wembley","1000","NWB"
"Norwood Junction","4003","NWD"
"Peckham Rye","4002","PMR"
"Penge West","4003","PNW"
"Queens Park","1000","QPW"
"Queens Road Peckham","4002","QRP"
"Rectory Road","-1","REC"
"Richmond","1001","RMD"
"Romford","1008","RMF"
"Rotherhithe","-1","ROE"
"Seven Sisters","-1","SVS"
"Shadwell","-1","SDE"
"Shepherds Bush","1002","SPB"
"Shoreditch High Street","-1","SDC"
"Silver Street","-1","SLV"
"South Acton","1001","SAT"
"South Hampstead","1000","SOH"
"South Kenton","1000","SOK"
"South Tottenham","1003","STO"
"Southbury","1007","SBU"
"St James Street","1006","SJS"
"Stamford Hill","-1","SMH"
"Stoke Newington","-1","SKW"
"Stonebridge Park","1000","SBP"
"Stratford","1001","SRA"
"Surrey Quays","-1","SQE"
"Sydenham","4003","SYD"
"Theobalds Grove","1007","TEO"
"Turkey Street","1007","TUR"
"Upminster","1008","UPM"
"Upper Holloway","1003","UHL"
"Walthamstow Central","1006","WHC"
"Walthamstow Queens Road","1003","WMW"
"Wandsworth Road","4002","WWR"
"Wanstead Park","1003","WNP"
"Wapping","-1","WPE"
"Watford High Street","1000","WFH"
"Watford Junction","1000","WFJ"
"Wembley Central","1000","WMB"
"West Brompton","1002","WBP"
"West Croydon","4003","WCY"
"West Hampstead","1001","WHD"
"White Hart Lane","-1","WHL"
"Whitechapel","-1","ZLW"
"Willesden Junction","-1","WIJ"
"Wood Street","1006","WST"
"Woodgrange Park","1003","WGR"
There is also a virtual line the “ELL Core” which is these stations
"DLJ","Dalston Junction"
"SQE","Surrey Quays"
"ROE","Rotherhithe"
"WPE","Wapping"
"SDE","Shadwell"
"HOX","Hoxton"
"HGG","Haggerston"
"ZCW","Canada Water"
"ZLW","Whitechapel"
"SDC","Shoreditch High Street"