Clear workflow for supporting custom shapefiles

[AA-Turner]

What problem would this feature solve? Please describe.
It is currently very difficult to add custom shapefiles to the programme (i.e. non-ONS). This would be of use for e.g. adding district shapes fron a cannonical source, and calculating statistics on a district basis

Describe the solution you'd like
A defined API or process to add external shapefiles

Additional context
Currently working on this for North Yorkshire

[AA-Turner]

Current status: adding custom shapefiles is easy. What is hard is creating the mapping between said shapefiles and the Census on the fly (this isn't a problem for the ONS, as the ONS PD is a pre-calculated map of postcodes to various codes - the type of thing we need to make dynamically here).

It is possible to do e.g. via a spatial join of meeting places and custom polygons, but a design decision is needed as to if this will be purely preprocessing or could be done on-the-fly.

I am probably leaning towards preprocessing at this moment in time.