On 09/03/2011 12:59, Leigh Caldwell wrote:
First, thanks again to the MySociety devs for the extremely useful MapIt
API which we've now been using for six or nine months.
:-)
I see that there is some data loaded for generation 15, which contains
the new Scottish Parliament boundaries that will be used from May 2011.
Yes.
However it appears that this does not contain a copy of the generation
14 data
No, because other boundaries are changing (e.g. quite a few councils;
only the Scottish Parliament future ones have been published) and it
would be wrong to state any knowledge about them yet. All we know about
the May 2011 Boundary-Line release for boundary changes at the 2011
elections are the Scottish Parliament boundaries that will exist from
that point, so that's all generation 15 currently contains.
> - so if we want to have full data from May onwards, do we need
to do two queries, using generation 15 for Scottish Parliament and then
generation 14 for all other boundaries?
When the May Boundary-Line is released and we import it into our system,
generation 15 will contain everything as it stands in that release, and
will become the active generation. Generation 14 will retire, as it were.
Before then, if you wish to know the current boundaries, you request
without a generation or with generation 14 (same thing at present), and
if you wish to know the Scottish Parliament future boundaries, you
request with generation 15. If you're using this data, please be
explicit about what is happening, as people can get quite confused about
what constituency they are, and then will be, in - especially as some
representatives don't appear to help the matter by telling people
they've already changed constituency before the election...
Is there a general way to determine, for any particular postcode or
area, what is the latest generation of data available for each area
type?
No, that's not something that should be used - you must explicitly
understand what is happening with respect to future boundaries and that
sort of thing would just lead to confusion. The Scottish Parliament
boundaries do not yet exist, so lumping them in with existing boundaries
would be confusing. Mapit will always return current data without a
generation, that is the latest available live data.
Presumably after May we can just omit the generation parameter and it
will return the latest data for each boundary?
Without a generation, it will return the active data, which is the
current live boundaries as it understands them, yes.
ATB,
Matthew
P.S. Just to be clear, the generation parameter works for large scale
boundary changes (e.g. the Scottish Parliament you mention, UK
Parliament before last election, or a council which has complete ward
redrawing), but small changes to boundaries that don't assign a new ONS
(or similar) ID just update the area, so the old slightly-changed
boundary is lost. That's just how it was written back in the day; a
different service could actually just store all boundaries each time, or
compare the geometries and store any differences, but it doesn't.
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