We're quite regularly asked why our catchment indicators do not match exactly the data shown on local authority websites. The short answer is because they are showing slightly different things. The long answer is below.

The problem with local authority data

One of the problems we came across early on, when building the site, was that whilst some local authorities publish cut-off distances (aka last distance offered), others don’t and the ones that do don’t always publish for all schools. Plus, the information is presented in a myriad ways, with each local authority having their own maps, pdfs and web pages; all presenting the data in slightly different ways.

We quickly realised that we weren't going to be able to work with this data for the 30k+ schools that we hold data on; it would require simply too much manual analysis and data entry. So, we investigated alternative sources of information.

The school census

After some failed attempts with Freedom on Information requests, we ended up turning to the school census, which is essentially a database of all children in England; including where they live and what school they go to.

Because we could see where existing pupils lived and break that down by year group, we were able to plot where the latest intake of children live on our map.

The application process for access to this data is rightly long and arduous, as it is highly sensitive information about our children, but we made our case for the public benefit and following approval by an ethics committee were granted access.

The school census provides consistent data for all schools across England, which we can work with. Because we can see where existing pupils live, we are able to plot where the latest intake of children live on our interactive map. There is more detail on exactly how we do this in our blog article Locrating's catchment areas explained.

A crystal ball

The theory is that by showing where the most recent intake of pupils live, with the ability to look back in time over a number of years, we can provide a reasonable indication as to where future pupils will likely live. Which is useful for people considering moving to an area or when looking for schools their children in their local area. However, this comes with a few very important caveats.

The past is not a predictor of the future!

The biggest of all is that the past is not a predictor of the future. As a perfect example, we have friends who have neighbours on either side of them whose children attend our friends' preferred school. These children where accepted in years before and after our friends applied for their child and yet our friend's child was not offered a place, why? Because it just so happened that in the year our friend's child applied, more children lived closer to the school than in the years before and after; just bad luck!

So many factors are in play that it's impossible to guarantee entry based on an address. We have an interesting article on these issues in our blog post catchment area myths.

What do the local authority data show?

Going back to the local authority data, some, but not all schools will offer a place to siblings over distance (amongst a range of different admissions criteria that schools may have, even including lotteries!) and this is where the local authority data can be very helpful, because when they publish a distance based on the 'distance criterion' it has siblings excluded; in fact not just siblings, they exclude children in care, with SEN and all those that were offered a place not based on their distance from the school.

A 'distance criterion' cut-off distance from a local authority, is the distance of the last child who was offered a place based solely on their distance from the school.

This means that a 'distance criterion' cut-off distance from a local authority, is the distance of the last child who was offered a place based solely on their distance from the school.

What do Locrating's catchment area indicators show?

These show where all children, including siblings live, broken down by area and year group. It would be nice to have the option to be able to exclude siblings (where appropriate - remember not all schools have a sibling policy), but unfortunately the school census database does not have a sibling indicator (nor details of school admission policies).

Although they do exclude children in care and with SEN as those markers do exist in the data and those children are almost always offered a place above other children; so can be justifiably excluded.

The differences

So, both pieces of data are totally correct and both from official sources of information, but they show slightly different things. Also, they can not be collected at the same time.

Our catchment area indicators are calculated from census data, which is collected each spring. Unfortunately, the process of getting the data from the Department for Education via the Office for National Statistics, typically takes a minimum of 6 months (and up to a year!) hence we don't show spring's data until autumn/winter.

As an example, pupils starting in September 2019 (the 2019/20 academic year) won't show on the census until spring 2020 and won't appear on Locrating until autumn/winter 2020, depending how long the data application process takes. We would love for this process to be shorter, but it is totally out of our hands.

Whereas, last distance offered is available much sooner, typically a few months after offers are made, hence you can often find last distance offered for the current academic year, but our latest catchment area indicators are always for the previous academic year.

Differences between the two are usually down to one of the following reasons:

• Users comparing the latest published last distance offered with our catchment area indicators for the previous academic year; these are different years and hence completely different children.
• Users comparing the last distance offered for schools with a sibling policy (which excludes siblings) we our red catchment area (which includes siblings); so again you can't compare different groups of children and expect the same result.

So, does this mean the local authority data is more useful than Locrating's; not at all, because they show different and equally important pieces of information. Where possible you want to look at both!

Is one better than the other?

So, does this mean one piece of data is more useful than the other; not at all, because they show different and equally important pieces of information. Where possible you want to look at both!

Last distance offered is handy if you want to see the sibling effect, whilst our catchment area indicators give insight into where pupils actually live and in what concentrations; which can be especially important if the school has a priority area, e.g. it's on a local authority boundary.

In general, we find that for oversubscribed schools, when comparing the same academic years, our green shaded circles correlate quite closely to the last distance offered.

The really important bit!

At an absolute minimum, you should familiarise yourself with each school's admissions policy, which should be available on their website. Without knowing how a school processes its applications, you have no way to make any meaningful assessment of you chances of success when applying to the school, irrespective of our catchment area indicators or the last distance offered.

Author: Lewis Tandy