TL;DR
A GIS site appraisal brings planning designations, flood risk, title, access, catchment and planning history for a site into one place before you spend money on surveys, solicitors or an offer. It works best early, when you are choosing between sites, and it narrows down the expensive checks rather than replacing them.
“Site appraisal” means different things depending on who says it. To a developer it often means the financial appraisal: what the scheme is worth, what it costs to build and what that leaves to pay for the land. To a planning consultant it can mean an assessment of policy and planning risk, and to an engineer it means surveys. Each of them costs money and takes time, so it pays to be confident in the site before any of them starts.
A GIS site appraisal comes first. It gathers the spatial facts about a site, or a long list of candidate sites, from the published datasets that describe it, and puts them in one place. That tells you which sites are worth the expensive work and which questions that work needs to answer.
What a GIS site appraisal checks
The checks depend on what you plan to build or operate, although most appraisals cover the same core layers. Each is a dataset laid over the site boundary and its surroundings, which means it can be measured, recorded and repeated across every site you are considering.
Planning designations
Designations set the outer limits of what a site can be used for. Some rule a site out or make it much harder to develop, such as Green Belt, Sites of Special Scientific Interest, Special Areas of Conservation, scheduled monuments and ancient woodland. Others shape what is acceptable, such as conservation areas, listed buildings nearby, Article 4 directions that remove permitted development rights and tree preservation orders.
Much of this is now open. The government’s Planning Data platform publishes over a hundred planning and housing datasets for England, including conservation areas, Article 4 direction areas, tree preservation zones, Green Belt and flood risk zones, although it warns that the data may be incomplete and not yet cover all of England.1 Natural England manages MAGIC, which brings together authoritative environmental data from around thirty organisations,2 and Historic England publishes listed buildings, scheduled monuments, registered parks and gardens and battlefields as free GIS downloads.3 Where the national platform has gaps, the local planning authority’s own data fills them, which is why an appraisal records where each layer came from.
Flood risk
Flood risk affects whether a site can be developed at all, what a planning application needs to include and what it costs to insure. The Environment Agency’s Flood Map for Planning shows risk from rivers and the sea, whereas surface water risk sits in a separate service.4 An appraisal should check both.
Flood risk also changes how sites are compared. National planning guidance applies a sequential test, which steers development towards areas at lower risk of flooding and asks whether a proposal could go on a lower-risk site that is reasonably available instead. Those alternative sites do not need to be owned by the applicant.4 If a site sits in a flood zone, the appraisal is the point at which you find out whether lower-risk alternatives exist in the same search area, before the planning application has to argue the case.
Title and ownership
HM Land Registry publishes INSPIRE Index Polygons free of charge, showing the indicative extent of registered freehold land in England and Wales.5 They show how many titles a site spans and where there may be unregistered land in between. A site in one title and the same area across six titles are very different acquisition problems, and an appraisal makes that visible early. The polygons are indicative, so the title register and title plan are still needed to confirm boundaries, rights and restrictions, and a solicitor should review those before anything is signed.
Access and catchment
Whether a site works often depends on who can reach it. Access means the physical route in: road frontage, visibility, distance to the nearest junction, public transport and anything that would make vehicle access difficult. Catchment means the people or businesses within reach, usually measured as a drive time or walk time rather than a straight-line distance, because a river or a motorway can put a site that looks close on a map a long way from the people it is meant to serve.
Census data is the usual basis. Census 2021 output areas are the smallest census geography, built to hold between 40 and 250 households,6 which is fine-grained enough to count the population within a fifteen-minute drive and describe it by age, household type or car ownership. For a leisure operator that might mean the number of adults within a given drive time; for a housing developer it might mean the age profile of the surrounding area and its growth since the last census.
Planning history and context
What has been applied for on and around a site says a lot about what is likely to be approved. Previous refusals, withdrawn applications and appeal decisions all bring out problems that the designations alone do not show. There is no single complete national dataset of planning applications, so this layer is usually assembled from each local planning authority’s own portal, and it takes longer to collect than any other.
Local authorities in England also publish brownfield land registers listing previously developed sites they consider appropriate for housing. The registers must be reviewed at least once a year and published as open data.7 For residential developers they are a useful source of candidate sites as well as a check on how the authority views a particular piece of land.
What the imagery shows
Datasets lag behind what is on the ground. Aerial and satellite imagery shows the things the data misses: a new building, a car park that is now a construction site, an access road that turns out to be a private track, a neighbouring use that changes the character of the area. In a systematic imagery review every site is checked against the same questions and the answers are recorded, so the rest of the team can see what was looked at and what was found.
One site or a hundred
A single-site appraisal answers the question “should we take this site further, and what should we ask next?” It is useful when a site has come to you through an agent or a landowner and you need to know quickly whether it is worth an offer or a survey.
The method saves the most time when it is applied to many sites at once. The same checks are run across every candidate, with hard constraints used to rule sites out and the remaining criteria weighted and scored. A long list of two hundred venues or land parcels becomes a shortlist of ten, and the reasons each site was kept or dropped are recorded alongside it. We set out that process step by step in last week’s post on GIS site selection, and our post on renewable energy site selection shows the same two-pass logic applied to solar.
We recently did this for an operator that places its units at host venues rather than on its own land. The long list was built from venue data, each venue was scored on catchment, access and the space available, and every shortlisted venue was reviewed against satellite imagery to confirm the space was there. The operator then reviewed the shortlist in a web map, marking each venue to approach or dismiss, so that the decisions sat on the map alongside the evidence for them.
What you get at the end
The outputs depend on how the appraisal will be used, although most include:
- A map pack showing each site against the constraints that apply to it
- A constraint summary for each site, recording what was found, the source and the date it was checked
- A scored shortlist with the weights used, where several sites are compared
- A list of open questions for the surveyor, solicitor or planning consultant
- The data itself, in a format your team can open, or an interactive web map where several people need to review sites
Recording the source and date of every layer makes the appraisal easier to maintain. Flood maps, title data and planning datasets are updated regularly, so a shortlist built six months ago may no longer be right; with the sources and dates recorded, the appraisal can be refreshed rather than redone.
When to commission one
A GIS site appraisal is worth doing when the cost of looking at the wrong site is high. That usually means one of these situations:
- You are choosing between several sites and need a consistent basis for comparing them
- You are about to commit money to a site, whether through an offer, an option agreement or a set of surveys
- You are planning a rollout and need to find suitable locations across a region or the whole country
- A site has come to you quickly and you need to know within days whether it is worth pursuing
It is less useful once the site is chosen and the questions are about detailed design. By then the surveys and the planning work carry the decision.
What it does not replace
A GIS appraisal is a desk-based screen. It narrows the field and sharpens the questions; however, it does not replace a site visit, a solicitor’s review of title, ground investigation, ecological survey or pre-application advice from the local planning authority. Its value is that those steps are spent on fewer sites, with a clearer idea of what each one needs to answer.
It also depends on the data behind it. Where national datasets are incomplete, or a local authority publishes its constraints in a format that needs cleaning, the appraisal should say so rather than treat missing data as the absence of a constraint.
How we approach site appraisals
Our site selection case study shows a working site selection application built in three weeks, and our property GIS data review shows the data work that sits underneath an appraisal. Our property and land page sets out how we support developers, landowners and operators, and the Knowledge Hub covers the GIS methods in more depth. If you are new to the open datasets mentioned above, our post on open data in the UK is a good place to start.
If you are weighing up one site or a long list and want the constraints in one place before you commit money, get in touch.
References
- Ministry of Housing, Communities and Local Government. Planning Data: datasets.
- Natural England. MAGIC.
- Historic England. Open Data Hub.
- Department for Levelling Up, Housing and Communities and Ministry of Housing, Communities and Local Government. Flood risk and coastal change.
- HM Land Registry. Use land and property data: INSPIRE Index Polygons.
- Office for National Statistics. Census 2021 geographies.
- Ministry of Housing, Communities and Local Government. Brownfield land registers.