Guidance from the GLA for choosing models in Witan to submit for the SRP

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How do I produce a ‘standard’ set of population projections?

One hurdle that users have come across is that they weren’t sure how to set up the models to produce a standard set of outputs such as they would have received from the GLA.

The default options the GLA would generally recommend to use are the Housing-Linked model, the Capped Household Size variant and Standard Fertility fertility assumption (for more information on what these mean, have a look at this post). If in the past, you have found the ‘Alternate’ variant roll projections to be a better fit for your local authority, then using the Trend-based projection and the Standard Fertility setting will replicate this.

When uploading your development data in the template, the GLA would recommend making sure that data is included for all years, including estimated development for 2011-2014. If you don’t have alternative estimates for these years, the SHLAA template that can be downloaded from the system includes estimated completions from the London Development Database.

Who should run the population projections in Witan?

This is up to each authority to determine for themselves. However, the GLA expects and generally encourage nominated Demography contacts to take a lead on this activity.

  • If you are unclear who is the Demography contact in your local authority, please let the GLA know and they’ll be happy to confirm.
  • If you’d like to know who are registered users of the system, drop Mastodon C a line and they can tell you.
  • If you are the nominated contact for your authority, but don’t feel confident in producing projections in Witan, please either Mastodon C or GLA know and we’ll be happy to assist.

GLA contact: Demography@london.gov.uk

Mastodon C contact: witan@mastodonc.com

Can I get roll projections without providing population projections?

If you have provided roll data, but are still struggling to create your population projections, the GLA can now produce a set of roll projections for you using their publicly available SHLAA-based projections. They still recommend producing your own projections that incorporate your most up to date development assumptions.