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A new PIN working paper, a new thread
There's a lot of debate and analysis about the nature of spatial disparities across Britain, and a lot of the answers people reach are partly due to the spatial units they use. These sound a lot like 90s magazine titles: LADs, NUTS, PUAs etc.
All of these have flaws when used for economic analysis, to the point that last year we decided that we were going to build our own from scratch. We based our new definitions on a central idea:
After a lot of experimentation, we divided British LSOAs into three categories of employment density:
If you map this it looks like this:
Next step was to identify the biggest groupings, or aggregates, of high density and medium density activity. We had to introduce a cut-off here: again after more experimentation we settled on 10,000 total jobs for medium density aggregates and 5,000 total jobs for high density.
There were 184 medium density areas, and 597 high density areas: we call these "cores" - they're shown in technicolour below (better resolution available in the report):
We were also interested in where the people who worked in these cores lived: so we mapped commuting zones, which we defined as the area around each core within which 25% of the residents in work, work in that core. We marked these with lines rather than solid blocks of colour.
ok - some examples of why this is useful: the PUAs around the Liverpool-Manchester region look like this:
which simultaneously misses the underlying detail revealed by our high density definitions:
and also the bigger picture revealed in our medium density map: that the Liverpool-Manchester region really is one big employment zone:
A different example, Cambridge: the various spatial layers of the Cambridge economy are shown in blue and black. The PUA (red line) is also shown, but far, far too small, the TTWA (orange line) is far too big: both are totally hopeless at capturing what's happening in reality.
Finally, Nottingham and Derby. Here's what the underlying economic patterns of the area looks like. The Nottingham economy is relatively tightly defined to the west, and spills out further to the east.
But the PUAs looks like this. Crazy, huh? Nottingham PUA is totally misaligned to its underlying economic geography, doesn't even capture all of its central employment core, and inadvertently captures a big chunk of Derby's commuting zone. Again - totally useless.
this isn't the end of the research thread - we're already looking at spatial employment patterns within our cores and commuting zones and the relationship to transport networks, agglomeration and productivity, as well as writing a follow up paper on polycentric urban areas.
Finally we have a database of statistics for all four categories (high/medium density, cores/commuting zones) we've used, that we're happy to share with other researchers, as well as the GIS shapefiles and definitions.
