Boundary Files for Electoral Wards Covered by a Particular Geography

A week or so ago, I went looking for boundary lines for UK electoral wards, with half a mind towards trying to do something with them related to this week’s local council elections. One source I came across was the UK 2011 Census, (2011 Census geography products for England and Wales) which publishes the appropriate data from across England and Wales in large single shapefiles. For the amateur cartographer (which I very much am!) wanting to work at a local level, this presents something of a challenge: not only do I have to find a way of downloading and opening the large dataset, I also need to find a way of extracting from it the data for my local area, which is what I actually want. (Getting the local data from the national dataset can be blocking, in other words.)

Another source of data is MySociety’s MapIt service, which provides data about various geographies, including electoral wards, covered by other geographical areas:

as well as boundary files for each geography in a variety of formats:

Unfortunately, the MapIt API doesn’t (yet?!) support the ability to generate a single file that contains boundary data for all the electoral wards in a single council or local authority area. So here’s a quick hack, posted as a view on Scraperwiki, that generates a single KML file for the electoral wards contained by a council area (including the wider boundary of that council area) – KML Merge Test. (There are probably better ways of doing this?! I would if I should try to make sense of the MapIt code to see if I can work out how to submit a proper patch…)

import scraperwiki,simplejson,urllib2
from lxml import etree
from copy import deepcopy


#--via @mhawksey
# query string crib https://views.scraperwiki.com/run/python_querystring_cheat_sheet/?
import cgi, os
qstring=os.getenv("QUERY_STRING")

key='65791' #Use the Isle of Wight as a default
typ='UTE'
#typs are:
#CTY (county council), CED (county ward), COI (Isles of Scilly), COP (Isles of Scilly parish), CPC (civil parish/community), CPW (civil parish/community ward), DIS (district council), DIW (district ward), EUR (Euro region), GLA (London Assembly), LAC (London Assembly constituency), LBO (London borough), LBW (London ward), LGD (NI council), LGE (NI electoral area), LGW (NI ward), MTD (Metropolitan district), MTW (Metropolitan ward), NIE (NI Assembly constituency), OLF (Lower Layer Super Output Area, Full), OLG (Lower Layer Super Output Area, Generalised), OMF (Middle Layer Super Output Area, Full), OMG (Middle Layer Super Output Area, Generalised), SPC (Scottish Parliament constituency), SPE (Scottish Parliament region), UTA (Unitary authority), UTE (Unitary authority electoral division), UTW (Unitary authority ward), WAC (Welsh Assembly constituency), WAE (Welsh Assembly region), WMC (UK Parliamentary constituency)

if qstring!=None:
    get = dict(cgi.parse_qsl(qstring))
    if 'key' in get: key=get['key']
    if 'typ' in get: typ=get['typ'] 
#---


#Get a stub KML file for the local council level
url='http://mapit.mysociety.org/area/'+str(key)+'.kml'
xmlraw = urllib2.urlopen(url).read()
xml=etree.fromstring(xmlraw)

#Get the list of electoral wards covered by that council area
wards=simplejson.load(urllib2.urlopen('http://mapit.mysociety.org/area/'+str(key)+'/covers?type='+typ))

#Get the KML for each ward, extract the Placemark data, and add it to our comprehensive KML tree
for ward in wards:
    url='http://mapit.mysociety.org/area/'+ward+'.kml'
    xmlraw = scraperwiki.scrape(url)
    xml2=etree.fromstring(xmlraw)
    p= xml2.xpath('//geo:Placemark',namespaces={'geo':'http://www.opengis.net/kml/2.2'})
    xml.append( deepcopy(p[0] ))

scraperwiki.utils.httpresponseheader("Content-Type", "text/xml")
print etree.tostring(xml)

The key value is the ID of the council area within which you want to find the electoral wards. So for example the Isle of Wight parliamentary constituency page -http://mapit.mysociety.org/area/65791.html – gives us the ID 65791, which we pass as an argument to the Scraperwiki view. The subdivision we want to grab data for is given by the typ parameter:

CTY (county council), CED (county ward), COI (Isles of Scilly), COP (Isles of Scilly parish), CPC (civil parish/community), CPW (civil parish/community ward), DIS (district council), DIW (district ward), EUR (Euro region), GLA (London Assembly), LAC (London Assembly constituency), LBO (London borough), LBW (London ward), LGD (NI council), LGE (NI electoral area), LGW (NI ward), MTD (Metropolitan district), MTW (Metropolitan ward), NIE (NI Assembly constituency), OLF (Lower Layer Super Output Area, Full), OLG (Lower Layer Super Output Area, Generalised), OMF (Middle Layer Super Output Area, Full), OMG (Middle Layer Super Output Area, Generalised), SPC (Scottish Parliament constituency), SPE (Scottish Parliament region), UTA (Unitary authority), UTE (Unitary authority electoral division), UTW (Unitary authority ward), WAC (Welsh Assembly constituency), WAE (Welsh Assembly region), WMC (UK Parliamentary constituency)

So for example, here’s a link to an aggregate KML file for Unitary authority electoral divisions (UTE) on the Isle of Wight – https://views.scraperwiki.com/run/kml_merge_test/?key=65791; and here’s one for Unitary authority wards (UTW) in Milton Keynes: https://views.scraperwiki.com/run/kml_merge_test/?key=2588&typ=UTW

If you save the resulting file as a .kml file (for example, as kml_merge_test_mk.kml) you can then load it into something like Google Fusion tables to view it:

Note that the MapIt API is rate limited (I think), so be gentle ;-)