The mapping process creates a random point within a building shell inside of a postcode area, which is repeated for every person in a postcode. This is in contrast to a simpler process, which does not take into account buildings at all, working simply with postcode areas. This can be seen in my previous post: Population of Scotland Mapped
In honour of the Forth Road Bridge re-opening completely. I created a map of the impact it has had on drive times from Edinburgh.
This is based on the OS Open Roads Product, using pgRouting, and network generated using the guide from Ross McDonald.
This does not take into account the increase of traffic on the other routes, or traffic in general. Would be interesting to see a real impact map from one of the major navigation providers.
Lets map the districts/regions/neighbourhoods/suburbs of Glasgow. The divisions of a city can be hard to distinguish, there are no hard boundaries between regions and these can be dynamic over time. Where does the West End begin? As soon as you cross the M8, or later? Where does the West End end? Before Partick, halfway through, or well past Scotstoun? Have your say!
Although Boston is a significantly easier target. Their map covered 21 different neighbourhoods. According to Wikipedia, Glasgow has at least 145 districts.
This will only be significant if we get a good number of responses. So please feel free to share!
This time I had a bit more time, staying overnight with the very accomodating girlfirend at the Barony Castle Hotel. The steak was excellent, but the sauna was not very hot. Overall a good experience though.
As you can see from the photos restoration works are in full progress.
And dontains can be made to the worthy cause at: MapaScotland.org
For a view of the way up to the map, see my first post on Mapillary:
For these I simply created multiple buffers using the QGIS buffer tool. This works for small samples, but was quite frustrating. I had initially hoped to do the whole analysis in SQLite, which worked pretty well initally, but struggled on the larger buffers. It took too long to run the queries, and did not allow for visualisation. I think using PostGIS would however be pretty feasible.
But creating a multi-ring buffer plugin for QGIS also seemed like a good learning experience. Which got me thinking, does it matter if you create increasingly large buffers around the original feature, or if you buffered the resulting buffer sequentially. My hypothesis was that there would be pretty significant differences due to the rounding of corners.
My question is not about the overlapping-ness of the buffers, since I think multi-ring buffers should be “doughnuts” anyway. But rather if smoothing will occur. The only answer was to try it myself.
Buffer styles:
Buffer the resulting buffer sequentially: Sequential
Buffer the original feature with increasing buffer distance: Central
[table caption=”Speed – In seconds”]
Features, Rings,Central, Sequential
1, 5, 0.59, 0.56
55, 5, 8.06, 6.38
1, 200, 60.83, 31.76
3, 200, 62.89, 40.89
55, 200, 628.38, 586.67
1, 2000, 203.84, 67.00
[/table]
No matter how you do it the sequential style is quicker, but that may be down to my code.
Rendering
Interestingly, although understandably, the sequential style results in a lot more vertices in the outer rings. For comparison, for a 500 ring buffer the outermost ring had the following vertice counts:
[table]
Style, Vertices
Central,488
Sequential,30918
[/table]
We can see this with editing turned on.
Central:
Sequential:
We can also see a smoother profile in the sequential buffer. However the difference is not major, and hard to discern with the naked eye.
So we have at most about around a 10m discrepancy, with 500 50m rings, so around 25000m of distance from the original feature.
This impacts rendering time dramatically, an example with our 500 rings:
Central:
Sequential:
So quicker to create but slower to draw. So which one is better, quicker calculation, or quicker rendering? Or should we not do 200+ ring buffers?
Hard to say. In version 0.2 of the Multi Ring Buffer Plugin. There is an option for either in the advanced tab.