22 July 2013 | Pierre Jenkins, Head of InstantAtlas Support
Using InstantAtlas to visualise rates and counts using Police Workforce data for England and Wales, March 2013
The Home Office have recently published their latest police workforce statistics on data.gov.uk.
This is a rich dataset with multiple tables and contains a mix of rates and counts. Having looked it over, I was interested in how InstantAtlas (IA) could be used to visualise this dataset, and in particular, cope with a mix of rates and counts in the same report.
A central issue with rates and counts is the type of map representation you use. Best practice dicates that rates/densities/percentages are shown using shaded areas whereas count data are better displayed using proportional symbols. The IA Double Map Time Series and Double Base Layer templates allow you to create both shaded area and proportional symbol maps in the same report to show a mix of rates and counts; an example is shown below.
An alternative approach, however, is not to map the counts at all but to show them in a supporting graphic instead. The Advanced Pie Chart component is ideal for this and I thought that the police workforce data would be a good way to showcase this chart.
The police workforce data were downloaded here. I had to carry out some simple manipulation in Excel to ensure that for each rate indicator, the correct count data was associated to it. This is illustrated in the screenshot below for the Total officers per 100,000 population indicator. The indicator values are in the leftmost column (C); these are the rates and will be used to draw the map. The associated count values are held in columns immediately to the right (D-J); these will be used to populate the pie chart with a breakdown of officers by rank when this indicator is selected.
I also added criminal offence data for April 2013 from www.ukcrimestats.com. The intention wasn't really to correlate this with the police workforce data but simply to provide some additional relevant data to showcase the Advanced Pie Chart.
In the IA Desktop Publisher, I chose the Single Map as my template, as this is the template that includes the Advanced Pie Chart. I used the Desktop Designer to insert the Advanced Pie Chart and then edited the settings to ensure that it would use associate values rather than indicator values as the source data.
There are lots of data titbits that can be extracted from these reports.
Example 1: the striking corridor of darker-shaded forces when you view the Minority ethnic officers as % of total officers indicator. While viewing this indicator, you can use the Advanced Pie Chart to compare ethnic breakdown and see that it is quite different, for example, for the Metropolitan and Leicestershire forces.
Example 2: out of a total force of 1,112 officers in Dyfed-Powys not a single one has stated their ethnicity as Black or Black British (the only force of 43 where this is the case).
Example 3: when viewing the Total offences indicator, the pie charts show the offences breakdown for Cleveland (the force with the highest crime rate for April 2013) to be quite different to that of the Metropolitan force, with over one in two offences being attributed to anti-social behaviour.
To sum up... putting the count data into the Advanced Pie Chart reports means that you can view the breakdown for any selected area, and then hover another area to make a comparison. The twin pies provide an effective way of making a quick visual comparision, and you can hover a segment of the chart to find out the actual count and associated percentage. The drawback is that you can't view the counts in a map; if this is your main purpose then using one of the Double Map templates mentioned above would be a better approach.