This page from GCHQ’s internal GCWiki, dated 24 April 2012 describes procedures for searching through financial data retained by the agency, and cites examples of some of its sources: see the Intercept article Airport Police Demanded An Activist’s Passwords. He Refused. Now He Faces Prison In The UK, 23 September 2017.
This 19-page NSA paper, delivered at the 2010 Five Eyes SIGDEV conference, gives a technical explanation of the importance of sourcing mobile carriers’ roaming agreements (IR.21): see the Intercept article Operation Auroragold: How the NSA Hacks Cellphone Networks Worldwide, 4 December 2014.
This excerpt from an NSA training manual shows the use of TAPERLAY and CHALKFUN tools. The former looks up the provider and country where a phone was first activated and the latter searches the FASCIA database to find a mobile phone’s past or current location: see the Washington Post article NSA tracking cellphone locations worldwide, Snowden documents show, 4 December 2013.