You saw the DEA do it with phone call records.
http://arstechnica.com/tech-po... Sept 4 2013
".... to place its employees in drug-fighting units around the country. Those employees sit alongside Drug Enforcement Administration agents and local detectives and supply them with the phone data from as far back as 1987.""
Thats just one tiny project with once set of data.
Water news
http://arstechnica.com/tech-po...
Power news
http://www.zerohedge.com/news/...
Thats just for one classic storage site thats in the news a lot.
Re So what would it really take to put this sort of thing together?
"The ultimate goal of the NSA is total population control" 11 July 2014
http://www.theguardian.com/com...
"At least 80% of all audio calls, not just metadata, are recorded and stored in the US, says whistleblower William Binney – that's a 'totalitarian mentality'"
Should give an average reader an idea of the US internal scale to store, track, index, search, voice print, call to, call from, other numbers, work back from hops surrounding people of interest.
ie well funded, all of the USA, over years, aspects of calls stored for years ready to be found in storage if seen at a protest, near a protest or near a person who was near a person at a protest.
ie you just need a lot of tame Room 641A like access
https://en.wikipedia.org/wiki/...