The public datasets behind automatic constraint checks

Automatic constraint checking is only as good as the planning constraint data sources underneath it, and every one of those datasets has a known edge it does not reach. The Flood Map for Planning says nothing about surface water. A listed building appears as a single point rather than a boundary. Tree preservation orders have no complete national coverage at all. None of that makes automated checking useless, but it does mean an architect who treats a green result as clearance is going to get caught.

PlanScope checks a site against Environment Agency flood data, Historic England listed buildings and conservation areas, and Natural England designated site layers, then feeds the results into its report recommendation engine. What follows is what each of those layers actually records, where the gaps sit, and how to close them before you commit a design.

Flood zone data and what it leaves out

The Flood Map for Planning is the map planning decisions are made against. It shows Flood Zone 2 and Flood Zone 3 for flooding from rivers and the sea, main rivers, flood storage areas and areas benefiting from defences. Zone 1 is everywhere else, defined by absence rather than by a polygon.

Two omissions matter on most sites. First, the national map does not distinguish Flood Zone 3a from Flood Zone 3b, the functional floodplain. That split is usually only available in the council's Strategic Flood Risk Assessment, and it is the difference between a site where housing may be acceptable with mitigation and a site where it is very unlikely to be.

Second, the map does not cover surface water. Pluvial flooding, groundwater and reservoir inundation sit on the separate long term flood risk service, and surface water is the source that causes most of the complaints about new development in urban areas. A site can be squarely in Flood Zone 1 and still sit in a critical drainage area with a documented history of water in the street.

So a flood flag of "Zone 1, no constraint" should be read as "no fluvial or tidal constraint identified from the national dataset". If the site is over one hectare, a Flood Risk Assessment is expected anyway regardless of zone, and that catches out more small developers than any other threshold.

Listed buildings are points, not boundaries

The National Heritage List for England is the statutory record, and it covers listed buildings, scheduled monuments, registered parks and gardens, registered battlefields and protected wreck sites. For listed buildings it is published as point data.

That single fact explains a lot of bad heritage screening. A point sits somewhere within or near the building it describes, and it tells you nothing about the extent of the listing. Curtilage structures, attached boundary walls, outbuildings and the interior are all protected without appearing anywhere on the map, and a scheduled monument or registered park is a polygon while the listed farmhouse inside it is a dot.

Distance from a point is also a poor proxy for effect on setting. A listed church tower 400 metres away across open ground may be far more sensitive to your proposal than a listed terrace 40 metres away behind a mature screen. Any automated distance test is a prompt to look, not an answer.

Read the list entry text rather than the map pin. The entry gives the grade, the date of listing, the description and, sometimes, an explicit statement about what is and is not included. Our note on searching the National Heritage List for a listed building covers how to get from a postcode to the entry, and where an entry is wrong there is a formal process for asking Historic England to amend it.

Conservation area boundaries are different again. They are designated by local authorities, so the authoritative version is the council's own map and designation document. The national planning data platform now aggregates boundaries supplied by authorities, and coverage is improving, but a missing boundary on a national layer is not evidence that no conservation area exists.

Designated site layers and impact risk zones

For ecology, the Defra MAGIC map is the usual starting point. It carries Sites of Special Scientific Interest, Special Areas of Conservation, Special Protection Areas, Ramsar sites, National Nature Reserves, the ancient woodland inventory, priority habitat inventory, National Landscapes and National Parks.

Two of those layers deserve a warning. The ancient woodland inventory was historically compiled for woods of two hectares and above, so small ancient woods and many veteran trees are simply absent from it. And the agricultural land classification available nationally is the provisional mapping at a coarse scale, which is why an Agricultural Land Classification survey of the actual soils is needed where best and most versatile land is in issue rather than a screenshot of the provisional layer.

The most useful layer for scoping is the Natural England SSSI Impact Risk Zones dataset. It shows where the designated sites are, and for each zone it also states which categories of development trigger consultation with Natural England. That lets you tell in one check whether your residential scheme, your infrastructure or your combustion plant is caught. Read the attribute text, not the colour.

What MAGIC will not tell you is whether the site itself supports protected species. Designations record what has been notified, and an unremarkable field with no designation can still hold a great crested newt population or a bat roost in the outbuilding. Our note on using MAGIC to find ecological designations near a site sets out the sequence, and the sequence always ends with a site walkover by an ecologist rather than with the map.

Tree protection is the worst-mapped constraint

Tree preservation orders are made by individual authorities under the Town and Country Planning (Tree Preservation) (England) Regulations 2012, and there has never been a complete national register. The national platform holds a partial dataset assembled from authority submissions, and the quality varies from mapped individual trees to a polygon showing the order area with no indication of which trees within it are protected.

Three practical consequences follow. An absence of a TPO record proves nothing, so ask the council directly. Where an order exists, the definitive document is the order itself with its schedule and plan, not a GIS layer. And every tree in a conservation area is protected regardless of any order, through the six-week notice requirement, which means a conservation area flag is also a tree flag.

Where trees are present, the survey that officers expect is a BS 5837 survey, and the tree survey needs to happen early enough to influence the layout rather than late enough to justify it.

Why the council's map and the national map disagree

Most of these designations are local acts recorded nationally. A council designates a conservation area or makes a tree preservation order, then supplies the geometry to a national platform at some later point. The national copy is a snapshot with a lag.

Add the ordinary mechanics of spatial data. Boundaries digitised from a paper plan carry the error of that plan. A centroid is not an extent. An order amended in 2019 may be represented by geometry captured in 2014. A ward boundary change or a local government reorganisation shuffles who holds the record.

None of that is a scandal, and it does not mean the national data should be ignored. It means the national layer is the screening tool and the authority's own register is the record. Where the two disagree on something that changes your design, the council's version governs and you should get their answer in writing.

Checking a flagged constraint at source

A flagged constraint deserves the same four steps every time.

1. Open the primary record. The list entry for a heritage asset, the designation document for a conservation area, the order and schedule for a TPO, the Strategic Flood Risk Assessment for a Zone 3 split, the citation for an SSSI.
2. Establish the extent, not the distance. Ask what is included in the designation and whether your site or its setting falls within it.
3. Ask the authority where the primary record is silent, by email, through the duty planner or as a pre-application question, and keep the reply.
4. Commission the survey where the constraint is about the site rather than about a boundary, because no dataset substitutes for a walkover.

Drafting tools insert a placeholder rather than inventing site facts, and a draft that arrives with "[TO BE CONFIRMED]" against a flood zone or a grade is telling you exactly which check has not been done. Treating those flags as a task list is the fastest way to use one, and the wider pattern of errors to look for is set out in our note on factual errors to look for in a drafted planning document.

Recording the check so it survives scrutiny

Constraint checks age. A flood map is republished, a conservation area is extended, an order is made on the oak at the back of the plot. If your submission asserts a constraint position, it should say when that position was established.

Record the dataset name, the date accessed and the query you ran, and keep the screenshot or export with the project file. Where the authority answered a question, keep the email. Where a survey established a fact, cite the report and its date. On a scheme that takes two years from feasibility to decision, this is the difference between answering a case officer's challenge in five minutes and rebuilding the evidence from scratch.

For anything where competence is legally required, such as protected species work or contaminated land, the data check is the start of the process and a suitably qualified professional has to do the rest. You can see who reviews and signs off drafted reports through the professional directory.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.