Regarding the street grid, living in London I could help you a little. The post code map you supplied at the start of the thread does not actually show London's real shape. The total area in the postcode map subtracted by the true size of London would equal an area more than a half (maybe even two thirds) of the size shown on the postcode map.
Either way, after you calculated the total size of your map then I'm guessing it's 2.3 miles on each side. I made a little street grid map to help you out with a few roads you may want to use. You can ignore it completely if you want (I don't mind ) but living in London I can show you some of the more important roads and some details about them.
These are merely suggestions from me, but I'd say it would be a very effective way of planning out the city. I've left many details I notice personally when I travel through these areas on the list.
Search up the roads and landmarks on Wikipedia or on Google Earth or StreetView to check them out, I think that using this street grid (only major roads included) would be a nice way to set out the city, but it is your choice - I just wanted to help you out!
(I took the liberty of widening out your original map. Hopefully the area that isn't water will become land in future versions because the London shape you used isn't ideal in my opinion. My placements of landmarks and roads on your map was influenced by their real life position and how they would fit and scale on your map.) Key:
It looks a bit complicated, but this key should help you out. Anything blue
is a motorway. Anything green
is a major A road. Anything light green
is a less important A road. Anything red
are suggestions from that you could use to fill up your map.
The black outline is what I'm guessing are the boundaries of the map you will use. I superimposed my diagram on a snapshot of your map that you took earlier in the year.
1. The M25 - It's obviously a ring road around London. My guess is that the M25 will hug the edges of your map in the finished version.
2. The A13
3. The A2
4. The A20
5. The A23
6. The A3 - Goes through Richmond Park (#14).
7. The M4 - This is one of the most important motorways in England. It spans from London to Wales. In London, the motorway starts where the A4 (#21 on the map) ends. This area is called the Chiswick roundabout, and the North Circular and South Circular (#16) meet here, so it's a very important junction. Also, the M4 starts as an elevated motorway where the flat A4 ends. You might want to have some sort of flyover here for the M4.
8. A4020 - This is also a pretty important road in the West of London. It's all flat, and there is nice suburban housing all around it. It ends at Shepherd's Bush. Shepherd's Bush is home to Europe's largest shopping mall, Westfield (#22 you might want to add this to the map as well).
9. A40 - Possibly the most important road in West London, also known as Westway, is an elevated A road that is often thought of as a motorway (after leaving the M25 it indeed turns into a motorway officially). It ends when it reaches the "Central London Ring Road" (#15 this isn't a real road, but actually many roads that join together in the Centre of London to make a "ring road like shape". The A40 is elevated until it is adjacent to the east edge of Hyde Park.
10. Hyde Park - Obviously, this is the most famous park in London. It is just west of the centre of London. It has a river-like lake, many ponds, trees and open spaces. To fit it inside the map, I placed it inbetween the A4020 (#8) and the A4 (#21).
11. These are just a few modern buildings off the A40. They look really nice, and it would be nice to have them modelled if you wanted to have some good scenery. Check out the end of the A40 on Google Street View to check them out.
12. South Acton & Brentford Estate - These are two infamous West London council estate with many ugly concrete tower blocks. Both estates are a shambles and I used to live in one of them. In the Brentford Estate (corresponding roughly on the western half of my shaded area), there are about 4 clone tower blocks probably reaching 80m. The South Acton estate meanwhile averages at around 30m per tower block, but the area is disgusting. In real life, it is getting a nice modern refurbishment, but this could be a great place to have crime and gang missions on your map. Both are modeled on Google Earth already so check them out if you want.
13. Similar to #11, these are some nice modern buildings off the M4. In fact, Sega Europe's headquarters is here. These buildings are so cool somebody's modeled them in Sketchup and can be seen on Google Earth in 3D. They're practically right next to the Brentford Estate buildings.
14. Richmond Park - I wanted to use my previous idea of having an endless park representing Richmond Park to be the south-east border of the map (somebody had also mentioned something similar earlier in the post). Richmond Park is the largest park in London so I guess you'll have it one way or the other in your map.
15. Central London Ring Road - As aforementioned, not a single road but many. Everything inside is part of the borough of Westminister (almost). This is where Big Ben, London Eye and all that good stuff is.
16. North & Circular Ringroad - Two roads that circle inner London. Two very important roads in London, and almost every major road branches off it. Nearly all of it is flat road
(not elevated). The western and south-werstern portions of the road is particularly narrow while the North-Western, North and Eastern portions are very wide and are pretty much flat motorways.
18. Wembley Stadium - I'd say my suggested location would be an accurate place to put it. Just north off the North Circular (#16).
19. Trellick Tower- This is another council estate tower block, but I'm suggesting it for a single reason. Click on the link. Yeahh, it's some strange architecture. Seeing as its a tower block, it's a haven for crime and gangsters.
20. Thamesmead Estate - This is another council estate, and probably the most infamous in East London. It's been in many films, and it's an ugly piece of work just off the river.
21. A4 - Where the M4 turns into a motorway, this is an important A road in West London. The area around is good housing. It is a flat road.
22. Westfield Shopping Centre - An awesome modern shopping mall which is the largest in Europe! Could be a good one to model, although it's hard to fit into the map.
I spent about an hour or two on this map, so hopefully it will be of help to you! If you have any questions about the details of these landmarks, feel free to ask me because I visit them every day.
Hope it helps!