1. Using Django’s StreamingHTTPResponse for JSON & HTML

    A few of mySociety’s developers are at DjangoCon Europe in Cardiff this week – do say hello :) As a contribution to the conference, what follows is a technical look (with bunny GIFs) into an issue we had recently with serving large amounts of data in one of our Django-based projects, MapIt, how it was dealt with, and some ideas and suggestions for using streaming HTTP responses in your own projects.

    MapIt is a Django application and project for mapping geographical points or postcodes to administrative areas, that can be used standalone or within a Django project. Our UK installation powers many of our own and others’ projects; Global MapIt is an installation of the software that uses all the administrative and political boundaries from OpenStreetMap.

    A few months ago, one of our servers fell over, due to running entirely out of memory.

    “Digging, digging, oh what was I doing, can’t remember any more!”

    Looking into what had caused this, it was a request for /areas/O08, information on every “level 8″ boundary in Global MapIt. This turned out to be just under 200,000 rows from one table of the database, along with associated data in other tables. Most uses of Global MapIt are for point lookups, returning only the few areas covering a particular latitude and longitude; it was rare for someone to ask for all the areas, but previously MapIt must have managed to respond within the server’s resources (indeed, the HTML version of that page had been requested okay earlier that day, though had taken a long time to generate).

    Using python’s resource module, I manually ran through the steps of this particular view, running print resource.getrusage(resource.RUSAGE_SELF).ru_maxrss / 1024 after each step to see how much memory was being used. Starting off with only 50Mb, it ended up using 1875Mb (500Mb fetching and creating a lookup of associated identifiers for each area, 675Mb attaching those identifiers to their areas (this runs the query that fetches all the areas), 400Mb creating a dictionary of the areas for output, and 250Mb dumping the dictionary as JSON).

    “It’s using *how* much memory?!”

    The associated identifiers were added in Python code because doing the join in the database (with e.g. select_related) was far too slow, but I clearly needed a way to make this request using less memory. There’s no reason why this request should not be able to work, but it shouldn’t be loading everything into memory, only to then output it all to the client asking for it. We want to stream the data from the database to the client as JSON as it arrives; we want in some way to use Django’s StreamingHTTPResponse.

    The first straightforward step was to sort the areas list in the database, not in code, as doing it in code meant all the results needed to be loaded into memory first. I then tweaked our JSONP middleware so that it could cope when given a StreamingHTTPResponse as well as an HTTPResponse. The next step was to use the json module’s iterencode function to have it output a generator of the JSON data, rather than one giant dump of the encoded data. We’re still supporting Django 1.4 until it end-of-lifes, so I included workarounds in this for the possibility of StreamingHTTPResponse not being available (though then if you’re running an installation with lots of areas, you may be in trouble!).

    “I know how to fix this!”

    But having a StreamingHTTPResponse is not enough if something in the process consumes the generator, and as we’re outputting a dictionary, when I pass that dictionary to the json’s iterencode, it will suck everything into memory upon creation, only then iterating for the output – not much use! I need a way to have it be able to iterate over a dictionary…

    The solution was to invent the iterdict, which is a subclass of dict that isn’t actually a dict, but only puts an iterable (of key/value tuples) on items and iteritems. This tricks python’s JSON module into being able to iterate over such a “dictionary”, producing dictionary output but not requiring the dict to be created in memory; just what we want.

    “I’m fiendish, yay!”

    I then made sure that the whole request workflow was lazy and evaluated nothing until it would reach the end of the chain and be streamed to the client. I also stored the associated identifiers on the area directly in another iterator, not via an intermediary of (in the end) unneeded objects that just take up more memory.

    I could now look at the new memory usage. Starting at 50Mb again, it added 140Mb attaching the associated codes to the areas, and actually streaming the output took about 25Mb. That was it :-) Whilst it took a while to start returning data, it also let the data stream to the client when the database was ready, rather than wait for all the data to be returned to Django first.

    “Look how quickly I’m streaming!”

    But I was not done. Doing the above then revealed a couple of bugs in Django itself. We have GZip middleware switched on, and it turned out that if your StreamingHTTPResponse contained any Unicode data, it would not work with any middleware that set Content-Encoding, such as GZip. I submitted a bug report and patch to Django, and my fix was incorporated into Django 1.8. A workaround in earlier Django versions is to run your iterator through map(smart_bytes, content) before it is output (that’s six’s iterator version of map, for Python 2/3 compatibility).

    Now GZip responses were working, I saw that the size of these responses was actually larger than not having the GZip middleware switched on?! I tracked this down to the constant flushing the middleware was doing, again submitted a bug report and patch to Django, which also made it into 1.8. The earlier version workaround is to have a patched local copy of the middleware.

    Lastly, in all the above, I’ve ignored the HTML version of our JSON output. This contains just as many rows, is just as big an output, and could just as easily cripple our server. But sadly, Django templates do not act as generators, they read in all the data for output. So what MapIt does here is a bit of a hack – it has in its main template a “!!!DATA!!!” placeholder, and creates an iterator out of the template before/after that placeholder, and one compiled template for each row of the results.

    “If it won’t generate, I’ll just replace the middle with something that will!”

    Now Django 1.8 is out, the alternate Jinja2 templating system supports a generate() function to render a template iteratively, which would be a cleaner way of dealing with the issue (though the templates would need to be translated to Jinja2, of course, and it would be more awkward to support less than 1.8). Alternatively, creating a generator version of Django’s Template.render() is Django ticket #13910, and it might be interesting to work on that at the Django sprint later this week.

    Using a StreamingHTTPResponse is an easy way to output large amounts of data with Django, without taking up lots of memory, though I found it does involve a slightly different style of programming thinking. Make sure you have plenty of tests, as ever :) Streaming JSON was mostly straightforward, though needed some creative encouragement when wanting to output a dictionary; if you’re after HTML streaming and are using Django 1.8, you may want to investigate Jinja2 templates now that they’re directly supported.

    [ I apologise in the above for every mistaken use of generator instead of iterator, or vice-versa; at least the code runs okay :) ]

  2. Are you still in the same ward?

    You might not be in the ward you think you are. Due to ongoing boundary changes, many people will be voting within new wards this year. Confused? Fortunately, you can use our new MapIt-powered ward comparison site to see whether you’ll be affected by any new boundaries.

    Pop your postcode in at 2015wards.mysociety.org and if your boundary is changing you’ll see your old and new wards.

    These alterations are generally put in place by the Local Government Boundary Commissions, in an aim to even out the number of constituents represented by each councillor.

  3. FixMyStreet now covers Northern Ireland

    Since its launch in 2005, WriteToThem has always covered all parts of the United Kingdom, and the Northern Ireland Assembly was the first body added to TheyWorkForYou after the UK Parliament, in late 2006. So whilst we certainly have not ignored Northern Ireland, it had always been an irritant of mine (and a cause of infrequent emails) that FixMyStreet only covered Great Britain.

    This was due to the way it had originally been funded and set up, but those issues were in the past, due to a myriad of changes both internal and external, and it was now more a case of being able to find the resources to implement the necessary work. Late last year, mySociety worked with Channel 4 on the website for their series of programmes on The Great British Property Scandal. This used, in part, code similar to FixMyStreet to let people report empty homes, and it was required to work in all parts of the UK. So as part of that process, code was written or generalised that let aspects of FixMyStreet like the maps and place name lookup work for Northern Ireland locations.

    It’s taken a few months since then to allocate the time, but we’ve now been able to take the code written back then, add various other bits, and incorporate it into FixMyStreet – which now covers the 26 councils of Northern Ireland, and the central Roads Service. Issues such as potholes, graffiti, and broken street lighting can be reported to Antrim or Newry and Mourne as easily as Aberdeen or Wyre Forest, and just as in the rest of the UK you can sign up for alerts based around your location or to your council.

  4. FixMyStreet’s been redesigned

    FixMyStreet, our site for reporting things like potholes and broken street lights, has had something of a major redesign, kindly supported in part by Kasabi. With the help of Supercool, we have overhauled the look of the site, bringing it up to date and making the most of some lovely maps. And as with any mySociety project, we’d really appreciate your feedback on how we can make it ever more usable.

    The biggest change to the new FixMyStreet is the use of responsive design, where the web site adapts to fit within the environment in which it’s being viewed. The main difference on FixMyStreet, besides the obvious navigation changes, is that in a small screen environment, the reporting process changes to have a full screen map and confirmation step, which we thought would be preferable on small touchscreens and other mobiles. There are some technical details at the end of this post.

    Along with the design, we’ve made a number of other improvements along the way. For example, something that’s been requested for a long time, we now auto-rotate photos on upload, if we can, and we’re storing whatever is provided rather than only a shrunken version. It’s interesting that most photos include correct orientation information, but some clearly do not (e.g. the Blackberry 9800).

    We have many things we’d still like to do, as a couple of items from our github repository show. Firstly, it would be good if the FixMyStreet alert page could have something similar to what we’ve done on Barnet’s planning alerts service, providing a configurable circle for the potential alert area. We also are going to be adding faceted search to the area pages, allowing you to see only reports in a particular category, or within a certain time period.

    Regarding native phone apps – whilst the new design does hopefully work well on mobile phones, we understand that native apps are still useful for a number of reasons (not least, the fact photo upload is still not possible from a mobile web app on an iPhone). We have not had the time to update our apps, but will be doing so in the near future to bring them more in line with the redesign and hopefully improve them generally as well.

    The redesign is not the only news about FixMyStreet today

    As part of our new DIY mySociety project, we are today publishing an easy-to-read guide for people interested in using the FixMyStreet software to run versions of FixMyStreet outside of Britain. We are calling the newly upgraded, more re-usable open source code the FixMyStreet Platform.

    This is the first milestone in a major effort to upgrade the FixMyStreet Platform code to make it easier and more flexible to run in other countries. This effort started last year, and today we are formally encouraging people to join our new mailing list at the new FixMyStreet Platform homepage.

    Coming soon: a major upgrade to FixMyStreet for Councils

    As part of our redesign work, we’ve spoken to a load of different councils about what they might want or need, too. We’re now taking that knowledge, combining it with this redesign, and preparing to relaunch a substantially upgraded FixMyStreet for Councils product. If you’re interested in that, drop us a line.

    Kasabi: Our Data is now in the Datastore

    Finally, we are also now pushing details of reports entered on FixMyStreet to Kasabi’s data store as open linked data; you can find details of this dataset on their site. Let us know if it’s useful to you, or if we can do anything differently to help you.

    Technical details

    For the web developers amongst you – we have a base stylesheet for everyone, and another stylesheet that is only included if your browser width is 48em or above (an em is a unit of measurement dependent on your font size), or if you’re running Internet Explorer 6-8 (as they don’t handle the modern CSS to do this properly, we assume they’ll want the larger styles) using a conditional comment. This second stylesheet has slight differences up to 61em and above 61em. Whilst everything should continue to work without JavaScript, as FixMyStreet has done with its map-based reporting since 2007, where it is enabled this allows us to provide the full screen map you can see at large screen sizes, and the adjusted process you see at smaller resolutions.

    We originally used Modernizr.mq() in our JavaScript, but found that due to the way this works (adding content to the end of the document), this can cause issues with e.g. data() set on other elements, so we switched to detecting which CSS is being applied at the time.

    On a mobile, you can see that the site navigation is at the end of the document, with a skip to navigation link at the top. On a desktop browser, you’ll note that visually the navigation is now at the top. In both cases, the HTML is the same, with the navigation placed after the main content, so that it hopefully loads and appears first. We are using display: table-caption and caption-side: top in the desktop stylesheet in order to rearrange the content visually (as explained by Jeremy Keith), a simple yet powerful technique.

    From a performance point of view, on the front page of the site, we’re e.g. using yepnope (you can get it separately or as part of Modernizr) so that the map JavaScript is downloading in the background whilst you’re there, meaning the subsequent map page is hopefully quicker to load. I’m also adding a second tile server today – not because our current one isn’t coping, it is, but just in case something should happen to our main one – we already have redundancy in our postcode/area server MapIt and our population density service Gaze.

    If you have any technical questions about the design, please do ask in the comments and I’ll do my best to answer.

  5. Mobile operators altering (and breaking) web content

    We had a complaint that FixMyStreet maps weren’t displaying on someone’s computer. We hadn’t had any other complaints, and we quickly narrowed it down to the fact that the person was on the internet using a tethered T-Mobile phone.

    T-Mobile (and Orange, and quite possibly others) are injecting JavaScript and altering content served over their networks. Their reason for doing this, according to their websites (T-Mobile, Orange), is to compress images and video sent to your browser, so as to speed up your browsing. Seeing it in action, they also inline some CSS and JavaScript, though not all, and remove comments from external files.

    However, their implementation breaks things. In this particular instance, the T-Mobile JavaScript comment stripper appears to be searching for “/*” and “*/” and removing everything inbetween. This might work in most cases; however in the jQuery library, we find a string containing “*/*”, and later down the file, another string containing “*/*”. T-Mobile remove everything between the things it thinks are comment markers, even though they’re actually contained within strings, causing the jQuery library to be invalid JavaScript and stopping anything using jQuery from running.

    Their decision to inline lots of the CSS also seems a bit odd – sure, on a mobile this might be quicker, but even ignoring tethering nowadays plenty of mobiles have caches too and having the CSS download once and be cached would seem better than adding weight to every page download. But I’m sure they’ve studied their decision there, and it doesn’t make any difference to the actual browsing, as opposed to the comment removal.

    To turn off this feature on your mobile phone or broadband, visit accelerator.t-mobile.co.uk or accelerator.orange.co.uk on your connection and pick the relevant option – if anyone knows of similar on other networks, do leave updates in the comments.

    From a FixMyStreet point of view – whilst FixMyStreet functions just fine without JavaScript, I had made the (perhaps incorrect) decision to put the map inside a <noscript> element, to prevent a flash of map-oddity as the JavaScript map overlaid the non-JS one. However, this meant in this circumstance the map did not work, as JavaScript was enabled, but jQuery was unable to be loaded. I haven’t decided whether to change this behaviour yet; obviously it would help people in this situation as the map would still display and function as it does for all those without JavaScript, but for those with JavaScript it does look a bit jarring as the page loads. Any suggestions on a better approach welcome :)

  6. Technical look at the new FixMyStreet maps

    This post explains how various aspects of the new FixMyStreet maps work, including how we supply our own OS StreetView tile server and how the maps work without JavaScript.

    Progressive enhancement

    During our work on FiksGataMi (the Norwegian version of FixMyStreet) with NUUG, we factored out the map code (for the Perlmongers among you, it’s now using Module::Pluggable to pick the required map) as FiksGataMi was going to be using OpenStreetMap, and we had plans to improve our own mapping too. Moving to OpenLayers rather than continuing to use our own slippy map JavaScript dating from 2006 was an obvious decision for FiksGataMi (and then FixMyStreet), but FixMyStreet maps have always been usable without JavaScript, utilising the ancient HTML technology of image maps to provide the same functionality, and we wanted to maintain that level of universality with OpenLayers. Thankfully, this isn’t hard to do – simply outputting the relevant tiles and pins as part of the HTML, allowing latitude/longitude/zoom to be passed as query parameters, and a bit of maths to convert image map tile clicks to the actual latitude/longitude selected. So if you’re on a slow connection, or for whatever reason don’t get the OpenLayers JavaScript in some way, the maps on FixMyStreet should still work fine. I’m not really aware of many people who use OpenLayers that do this (or indeed any JavaScript mapping API), and I hope to encourage more to do so by this example.


    We investigated many different maps, and as I wrote in my previous blog post, we decided upon a combination of OS StreetView and Bing Maps’ OS layer as the best solution for the site. The specific OpenLayers code for this (which you can see in map-bing-ol.js is not complicated (as long as you don’t leave in superfluous commas breaking the site in IE6!) – overriding the getURL function and returning appropriate tile URLs based upon the zoom level. OpenLayers 2.11 (due out soon) will make using Bing tiles even easier, with its own seamless handling of them, as opposed to my slight bodge with regard to attribution (I’m displaying all the relevant copyright statements, rather than just the one for the appropriate location and zoom level which the new OpenLayers will do for you). I also had to tweak bits of the OpenLayers map initialisation so that I could restrict the zoom levels of the reporting map, something which again I believe is made easier in 2.11.


    Having pluggable maps makes it easy to change them if necessary – and it also means that for those who wish to use it, we can provide an OpenStreetMap version of FixMyStreet. This works by noticing the hostname and overriding the map class being asked for; everything necessary to the map handling is contained within the module, so the rest of the site can just carry on without realising anything is different.

    OS StreetView tile server

    Things started to get a bit tricky when it came to being ready for production. In development, I had been using http://os.openstreetmap.org/ (a service hosted on OpenStreetMap’s development server) as my StreetView tile server, but I did not feel that I could use it for the live site – OpenStreetMap rightly make no reliability claims for it, it has a few rendering issues, and we would probably be having quite a bit of traffic which was not really fair to pass on to the service. I wanted my own version that I had control over, but then had a sinking feeling that I’d have to wait a month for something to process all the OS TIFF files (each one a 5km square) into millions and millions of PNG tiles. But after many diversions and dead ends, and with thanks to a variety of helpful web pages and people (Andrew Larcombe’s guide [dead link removed] to his similar install was helpful), I came up with the following working on-demand set-up, with no pre-seeding necessary, which I’m documenting in case it might be useful to someone else.

    Requests come in to our tile server at tilma.mysociety.org, in standard OSM/Google tile URL format (e.g. http://tilma.mysociety.org/sv/16/32422/21504.png. Apache passes them on to TileCache, which is set up to cache as GoogleDisk (ie. in the same format as the URLs) and to pass on queries as WMS internally to MapServer using this layer:


    MapServer is set up with a Shapefile (generated by gdaltindex) pointing at the OS source TIFF and TFW files, meaning it can map tile requests to the relevant bits of the TIFF files quickly and return the correct tile (view MapServer’s configuration* – our tileserver is so old, this is still in CVS). The OUTPUTFORMAT section at the top is to make sure the tiles returned are anti-aliased (at one point, I thought I had a choice between waiting for tiles to be prerendered anti-aliased, or going live with working but jaggedy tiles – thankfully I persevered until it all worked :) ).

    Other benefits of OpenLayers

    As you drag the map around, you want the pins to update – the original OpenLayers code I wrote used the Markers layer to display the pins, which has the benefit of being simple, but doesn’t fit in with the more advanced OpenLayers concepts. Once this was switched to a Vector layer, it now has access to the BBOX strategy, which just needs a URL that can take in a bounding box and return the relevant data. I created a subclass of OpenLayers.Format.JSON, so that the server can return data for the left hand text columns, as well as the relevant pins for the map itself.

    Lastly, using OpenLayers made adding KML overlays for wards trivial and made those pages of the site much nicer. The code for displaying an area from MaPit is as follows:

        if ( fixmystreet.area ) {
            var area = new OpenLayers.Layer.Vector("KML", {
                strategies: [ new OpenLayers.Strategy.Fixed() ],
                protocol: new OpenLayers.Protocol.HTTP({
                    url: "/mapit/area/" + fixmystreet.area + ".kml?simplify_tolerance=0.0001",
                    format: new OpenLayers.Format.KML()
            area.events.register('loadend', null, function(a,b,c) {
                var bounds = area.getDataExtent();
                if (bounds) { fixmystreet.map.zoomToExtent( bounds ); }

    Note that also shows a new feature of MaPit – being able to ask for a simplified KML file, which will be smaller and quicker (though of course less accurate) than the full boundary.


    *Broken link removed, Nov 2014

  7. Zoomable maps and user accounts on FixMyStreet

    Last week, FixMyStreet gained a number of new features that we hope you will find useful.

    Birmingham on FixMyStreetStroud on FixMyStreetFirstly, we’ve thrown away our old maps and replaced them with new, shiny, zoomable maps. This should make it easier for people to find and report problems, especially in sparser locations. We’re using the OS StreetView layer (hosted internally) when zoomed in, reverting to Bing Maps’ Ordnance Survey layer when zoomed out, as we felt this provided the best combination for reporting problems. In urban areas, you can still see individual houses, whilst in more rural areas the map with footpaths and other such features is probably of more use. FixMyStreet tries to guess initially which map would be most appropriate based upon population density, meaning a search for Stroud looks a bit different from that for Birmingham.

    FixMyStreet with OpenStreetMap

    OpenStreetMap fans, don’t worry – as part of our mapping technology upgrade, you can now use osm.fixmystreet.com to access your favourite mapping instead.

    Secondly, we now have user accounts. We’ve rolled these out alongside our current system of email confirmation, and it’s up to you which you use when reporting a problem or leaving an update. This means that those who come to the site one time only to report a pothole can continue to do so quickly, but have the option of an account if they want. Having an account means you no longer have to confirm reports and updates by email, and you have access to a page listing all the reports you’ve made through FixMyStreet, and showing these reports on a (obviously new and shiny) summary map.

    Adur District Council reports

    Other improvements include a much nicer All Reports section, so you can see all reports to Adur District Council on a map, paginated and with the boundary of the council marked – and individual wards of councils now each have their own pages too.

    I’ll follow up this post with another, more technical, look at the maps and how they work, for anyone who’s interested :)

  8. Upcoming business on TheyWorkForYou

    TheyWorkForYou has, until now, only covered things that have already happened, be that Commons main chamber debates since 1935, Public Bill committees back to 2000, or all debates in the modern Northern Ireland Assembly.

    From today, we are taking the UK Parliament’s upcoming business calendar and feeding it into our database and search engine, which means some notable new features. Firstly, and most simply, you can browse what’s on today (or the next day Parliament is sitting), or 16th May. Secondly, you can easily search this data, to e.g. see if there will be something happening regarding Twickenham. And best of all, if you’re signed up for an email alert – see below for instructions – you’ll get an email about any matching future business along with the matching new Hansard data we already send. We currently send about 25,000 alerts a day, with over 65,000 email addresses signed up to over 111,000 alerts.

    Mark originally wrote some code to scrape Parliament’s business papers, but this sadly proved too fragile, so we settled on Parliament’s calendar which covers most of the same information and more importantly has (mostly) machine-readable data. Duncan and I worked on this intermittently amidst our other activities, with Duncan concentrating on the importer and updating our search indexer (thanks as ever to Xapian) whilst I got on with adding and integrating the new data into the site.

    I’ve also taken the opportunity to rejig the home page (and fix the long-standing bug with popular searches that meant it was nearly always Linda Gilroy MP!) to remove the confusingly dense amount of recent links, bring it more in line with the recently refreshed Scottish Parliament and Northern Ireland Assembly home pages, and provide more information to users who might not have any idea what the site covers.

    Signing up for an email alert: If you want to receive an email alert on a particular person (MP, Lord, MLA or MSP), visit their page on TheyWorkForYou and follow the “Email me updates” link. If you would like alerts for a particular word or phrase, or anything else, simply do a search for what you’re after, then follow the email alert or RSS links to the right of the results page.

  9. Helping voters in the devolved elections

    As well as council elections and the referendum, the Scottish Parliament, Welsh Assembly, and Northern Ireland Assembly are holding elections this May. In Scotland and Northern Ireland, there are accompanying boundary changes, meaning this year you might be voting in a different constituency from last time.

    To help people, as we’ve again had a few requests, our service from the 2010 general election is back, at http://www.theyworkforyou.com/boundaries/, just for the Scottish Parliament and Northern Ireland Assembly. Our generic lookup service MaPit also provides programmatic access to these results (technical footnote).

    Alongside this service, we have refreshed our Scotland and Northern Ireland front pages, to slightly better display and access the wide array of information TheyWorkForYou holds for those devolved legislatures.

    Sadly the Scottish Parliament changed the format of their Official Report in mid January and we haven’t been able to parse the debates from then until its dissolution this March – hopefully we’ll be able to fix that at some point, and apologies for the inconvenience in the meantime.

    There don’t appear to be any central official lists of candidates in these elections. Amnesty.org.uk has a PDF of all candidates in Northern Ireland; David Boothroyd has a list of Scottish Parliament candidates. CAMRA appears to have lists for both Scotland and Wales. Those were simply found while searching for candidate lists, we obviously hold no position on those organisations :)

    Technical footnote: To look up the new Scottish Parliament boundaries using MaPit, provide a URL query parameter of “generation=15″ to the postcode lookup call. The Northern Ireland Assembly boundaries are aligning with the Parliamentary boundaries, so you can just perform a normal lookup and use the “WMC” result for the new boundary.

  10. New features on MaPit

    We’ve added a variety of new features to our postcode and point administrative area database, MaPit, in the past month – new data (Super Output Areas and Crown dependency postcodes), new functionality (more geographic functions, council shortcuts, and JSONP callback), and most interestingly for most people, a way of browsing all the data on the site.

    • Firstly, we have some new geographic functions to join touches – overlaps, covered, covers, and coverlaps. These do as you would expect, enabling you to see the areas that overlap, cover, or are covered by a particular area, optionally restricted to particular types of area. ‘coverlaps’ returns the areas either overlapped or covered by a chosen area – this might be useful for questions such as “Tell me all the Parliamentary constituencies fully or partly within the boundary of Manchester City Council” (three of those are entirely covered by the council, and two overlap another council, Salford or Trafford).
    • As you can see from that link, nearly everything on MaPit now has an HTML representation – just stick “.html” on the end of a JSON URI to see it. This makes it very easy to explore the data contained within MaPit, linking areas together and letting you view any area on Google Maps (e.g. Rutland Council on a map). It also means every postcode has a page.
    • From a discussion on our mailing list started by Paul Waring, we discovered that the NSPD – already used by us for Northern Ireland postcodes – also contains Crown dependency postcodes (the Channel Islands and the Isle of Man) – no location information is included, but it does mean that given something that looks like a Crown dependency postcode, we can now at least tell you if it’s a valid postcode or not for those areas.
    • Next, we now have all Lower and Middle Super Output Areas in the system; thanks go to our volunteer Anna for getting the CD and writing the import script. These are provided by ONS for small area statistics after the 2001 census, and it’s great that you can now trivially look up the SOA for a postcode, or see what SOAs are within a particular ward. Two areas are in MaPit for each LSOA and MSOA – one has a less accurate boundary than the other for quicker plotting, and we thought we might as well just load it all in. The licences on the CD (Conditions of supply of SOA boundaries and Ordnance Survey Output Area Licence) talk about a click-use licence, and a not very sraightforward OS licence covering only those SOAs that might share part of a boundary with Boundary-Line (whichever ones those are), but ONS now use the Open Government Licence, Boundary-Line is included in OS OpenData, various councils have published their SOAs as open data (e.g. Warwickshire), and these areas should be publicly available under the same licences.
    • As the UK has a variety of different types of council, depending on where exactly you are, the postcode lookup now includes a shortcuts dictionary in its result, with two keys, “council” and “ward”. In one-tier areas, the values will simply by the IDs of that postcode’s council and ward (whether it’s a Metropolitan district, Unitary authority, London borough, or whatever); in two-tier areas, the values will again be dictionaries with keys “district” and “council”, pointing at the respective IDs. This should hopefully make lookups of councils easier.
    • Lastly, to enable use directly on other sites with JavaScript, MaPit now sends out an “Access-Control-Allow-Origin: *” header, and allows you to specify a JSON callback with a callback parameter (e.g. put “?callback=foo” at the end of your query to have the JSON results wrapped in a call to the foo() function). JSONP calls will always return a 200 response, to enable the JavaScript to access the contents – look for the “error” key to see if something went wrong.

    Phew! I hope you find this a useful resource for getting at administrative geographic data; please do let us know of any uses you make of the site.