The theft hot spots map just looks like a map of where more cycle.
Surprised to see chains the most broken lock, although there's a massive "unknown".
Stands to reason that bike thieves are going to target bike-rich areas where plenty of choice exists and there is likely to be a larger number of carelessly unlocked or poorly secured bikes on offer to take.
Based on the means I see used to secure bikes, I'd say cable locks, very often of weedy quality, are by far the most common method used to secure bikes on-street in shopping areas and outside stations. Chains are probably in third place, behind cables, then D-locks.
The thing is, is the risk of theft mainly governed by the type of lock used, or the value and desirability of the bike? If I'm locking a hack bike on-street for a few minutes while I pop in a shop, I sometimes use a medium strength cable lock. If I'm leaving it for a couple of hours or more (say pub visit) I use the cable lock AND a 5/16" thick chain & padlock. I've not had one stolen yet, but we are talking about £20 secondhand bikes here, so not much criminal profit.