Shropshire electoral review using ArcGIS

Shropshire CouncilWhat are electoral reviews and why do one?

Electoral reviews are undertaken periodically and their main aim is to ensure that ‘electoral equality’ is maintained, meaning that all councillors in a single authority represent approximately the same number of electors.

Reviews are needed if there has been a lot of new development in an area which results in an increase in the numbers of electors or (as in the case of Shropshire) if a new authority is formed which has a different number of councillors, to ensure there are fair arrangements in place for the first elections to the new authority.

Shropshire electoral review

In preparation for becoming a unitary authority, Shropshire Council and the Boundary Committee for England carried out a review of local government electoral arrangements for Shropshire.

The electoral divisions of the former Shropshire County Council and the electoral wards of the former five district councils ceased to exist when Shropshire became a unitary authority on 1st April 2009.

The Committee looked at the number of councillors to be elected to the new council and also the boundaries of the individual areas they will represent. The new arrangements were selected and in place in time for the elections which were held on 4th June 2009.

All of the electoral divisions in Shropshire have changed, and the Council now has 63 electoral divisions which are represented by 74 local councillors (some areas have 2 councillors and one has 3).

How was this achieved?

Throughout the Shropshire electoral review ArcGIS 9.2 was used extensively to map boundaries, the electorate and dwelling completions.

All the calculations used in the forecasting process were also done using ArcGIS and the modelling function was used to carry out repetitive processes when producing each option.

Step 1: mapping existing boundaries

Initially a new shape file of boundaries was created for Shropshire to identify the constituent areas of the existing parishes and district wards.

This was achieved by overlaying the shape files of the existing district wards and parishes and creating an intersect shape file of parish wards. Each area was given a unique code, which was a combination of the parish and ward code.

Step 2: mapping the electorate

The district electoral rolls were geocoded in Access by matching the addresses against Address Point and the Local Land and Property Gazetteer and then mapped in ArcGIS.

The number of electors in each of the parish wards was calculated by joining the parish ward to the electorate shape file using the intersect function.

The electorate file was then summarised on the parish ward code to provide the total electors in each of these areas.

Step 3: mapping housing completions

The number of housing completions expected in the next five years was estimated, on a site by site basis, with the help of local planning officers. These were also mapped and summarised for parish wards in the same way as the electorate.

Dwelling completions were used in this study since they were thought to be the most robust method of estimating increases in the numbers of electors over the short term because other data, which might have been used to forecast increases in electors, was not available for small areas (i.e. migration data).

This method is simplistic but tight timescales precluded the possibility of developing a more sophisticated method.

An average number of electors per dwelling was calculated and applied to the number of new dwelling completions expected.

Map of housing developments
Housing developments

Step 4: forecasting elector numbers

The modelling function of ArcGIS was used to calculate an elector forecast and variance from the average.

An elector forecast is calculated to ensure that elector equality is maintained over the next five years or that areas are moving towards elector equality since this is one of the principle factors to consider in an electoral review. Otherwise, you may have to undertake more frequent reviews to redraw boundaries to maintain equality.

For example, some areas may be below the average number of electors to start with but in five years time would reach the average because of an increase in electors arising from new housing development.

Screenshot of model used within ArcGIS
Screenshot of model used within ArcGIS

Step 5

Once the Council size had been determined, a great number of options were produced in discussion with local members and parish councils.

Attribute fields were added to the parish ward shape file for each option and the dissolve by attribute function was used in ArcGIS to create an Electoral Division shape file for each option, along with a count of electors and completions in each area.

Maps were produced for each of the options and reproduced as paper copies or PDFs for consultation.

Maps from ArcGIS

ArcGIS proved to be an invaluable tool to test options efficiently and to extremely tight deadlines.

Find out more

The Boundary Committee’s final recommendations and maps are available on Shropshire Council’s site.

View all the reports relating to the Shropshire review.

Further information on the role of the Electoral Commission and Boundary Committee.

Thanks to Juliet Lane, Information & Research Manager at Shropshire Council for providing this article.

One Response

  1. Perhaps this explains how badly thought out were the boundaries. In the Bagley ward there was one group of houses about half a mile from the nearest part of the ward and entirely surrounded by Harlescott ward.

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