I'm looking for the best workflow for mapping postcodes and calculated territories, but being relatively new to mapping I'm struggling on a few details and also the best practices for displaying these maps via a browser.
I have access to the Code-Point Open postcode data from Ordnance Survey and my intention is to generate layers based on this data based on a series of dissolving aggregations (Postcode Sector into Group1 into Group2 into Group3) etc.
I think I need to aggregate this data in each level using Voronoi regions - what I don't understand is whether I need to generate polygons or can draw these polygons in a live manner?
I have access to Windows (WAMP) and Red Hat 6 (LAMP+PostGres+PostGis) - where can I find out more about generating voronoi and the advantages/disadvantages of pre-rendered polygons?
On a side note, our regions change quarterly and so for all but the lowest level this data will need recalibrating 4 times a year - we would probably regroup postcode sectors at the same time (as Code-Point is also updated quarterly and well, we might as well update everything).
Answer
OK, so I moved away from generating this polygon data directly in PostGIS and used qGis instead as it was better for my learning curve to see this happen visually, and the voronoi polygons contained far less errors and overlapping regions over the same sample than the various postgis algorithms I tested - here are the steps I took:
- Added a PostGIS layer for my point data, including sector attributes.
- Created Voronoi polygons in new layer based on the point data (Vector > Geometry Tools > Voronoi Polygons)
- Dissolved Voronoi layer into sectors layer based on attribute (Vector > Geoprocessing Tools > Dissolve)
- Created new outline layer as a mask to trim sectors that disappear to sea and use it as a clip mask to tidy sectors layer.
- Imported final shapefile into PostGIS direct from qGIS.
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