Don't go flying on that map; it's quite out of date - it doesn't have the Emirates air line on at Greenwich for a start. The routes are designed for, and mandated for, single engine types. The triangles are reporting points which you may receive partial clearances to or be asked to hold at. The bulk of the hashed area used to be known as the 'specified area'. Singles were verboten but twins could ask for direct transits; much to the chagrin of a trapper, once on a check ride we entered the lanes at the top of the Lea valley only to be cleared direct to Barnes for a H3 exit...straight over the City...
In many respects they are easier at night. Savoia's Godfather did a good job in laying down routes over parks/rivers/rails so if you just 'follow the dark area' you're seldom far off the right track. Just be wary that the LHR controllers can get very sensitive depending on which rwy is in use and how busy they are.
The extension of the LHR zone to the east is to cover London City airport. I think the 'dots' you refer to are stations.