Using historic maps to evidence a former land use

Historic Ordnance Survey mapping is the cheapest evidence you will ever buy about what happened on a site, and on a Phase 1 desk study it does most of the work. A sequence of editions showing a pond in 1899, a works in 1938 and level ground in 1962 tells you there is probably made ground under the northern half of the site, and it tells you before anyone has put a rig on it.

Used well, historic maps land use evidence builds the source side of a conceptual site model. Used badly, it produces a report that lists map editions and concludes nothing.

The map series you are working with

Two families of mapping cover most English sites.

The County Series runs from the mid nineteenth century, at 1:2,500 for cultivated and built-up areas and 1:10,560 for the rest, with a first edition surveyed county by county through the 1840s to 1890s and subsequent revisions into the 1930s. The National Grid series replaced it from the late 1940s, at 1:1,250 in urban areas, 1:2,500 elsewhere and 1:10,000 in place of the old six inch sheets.

Coverage is uneven. Rural sites may have four editions in 150 years, urban sites twelve. Wartime editions carry deliberate omissions of sensitive installations, which is a real gap rather than evidence of absence.

Note the difference between the survey date, the revision date and the publication date printed in the margin. A sheet marked as published in 1946 may have been revised in 1938, so the feature you are looking at existed some time before the earlier of those dates and may have gone by the later one.

Reading annotations without over-reading them

The annotations that matter on a contamination desk study are the industrial ones, and they are more specific than people assume.

Works, with a qualifier such as Gas Works, Chemical Works, Tannery, Tar Works, Iron Works or Printing Works. Depot, Sidings, Engine Shed and Tram Depot. Smithy, Foundry and Mill. Tanks, which appear as small annotated rectangles and are worth chasing across editions. Sewage Works and Filter Beds. Refuse Tip, Old Quarry, Gravel Pit, Clay Pit, Ballast Pit and Brick Works. Garage and, from the interwar period, petrol filling stations.

What these tell you is the type of process, not the substances used or how they were handled. A site annotated Works in 1912 with no qualifier is a prompt to look at trade directories, not a finding of contamination.

Be careful with two habits. Do not translate a nineteenth century annotation into a modern process description without evidence. And do not ignore the boundary of the annotated area, because a gas works label may sit over a plot that extends well beyond your red line, which changes whether the source is on site or off site.

Building the land use history edition by edition

Work through the editions in date order and record the same fields each time.

1. Edition, survey and revision dates, and scale.
2. On-site features and annotations, described by location within the site rather than generally.
3. Off-site features within a study radius, commonly 250 metres for a preliminary assessment, with the direction and approximate distance from the site boundary.
4. What changed since the previous edition, which is the column that actually drives the conclusions.
5. Anything that disappeared, which matters more than anything that appeared.

That last point is the one junior staff miss. A pond, a pit or a stream present on one edition and absent on the next has almost always been filled with something, and the something is rarely clean.

Spotting infilled ground and buried tanks

Four map signatures repay attention.

Water features that vanish. Ponds, mill races, moats, ox-bows and brick pits shown on an early edition and gone by a later one indicate infill. The extent of the original feature is your best estimate of the extent of the made ground.

Contour and spot height changes. Where a site rises by two metres between editions with no building added, material came from somewhere.

Annotated tanks, which appear and disappear without ceremony. An above-ground tank on one edition may have been replaced by an underground one that is never drawn at all.

Quarry and pit edges that migrate. Extraction followed by restoration is one of the most common histories for edge-of-settlement sites, and the restoration material is the question.

Cross-checking against other records

Map evidence on its own is a hypothesis. Three sources test it without much cost.

Aerial photography, including wartime and post-war vertical coverage, shows disturbed ground, stockpiles, tank farms and hardstanding that maps generalise away. Historic England holds and publishes aerial imagery for England.

Geological mapping and borehole records from the British Geological Survey give you the natural sequence and, where logs exist, direct observations of made ground thickness. A borehole 80 metres away is worth more than any inference from a map.

Trade directories and local studies collections at the county record office name the occupier and the trade, which is how Works becomes electroplating works. This is slow work and it is the part that turns a generic report into a specific one.

Where map evidence runs out

Maps are a plan view of the surface at intervals of decades. They say nothing about what was stored, spilled, buried or piped.

They miss short-lived uses entirely. A wartime fuel depot that operated for four years between revisions leaves no cartographic trace. They generalise, so small structures are omitted at 1:10,560 that appear at 1:2,500. And georeferencing introduces its own error, so a digitally overlaid historic sheet can sit several metres off the modern survey, which matters when you are locating a tank.

So a desk study built only on maps cannot support a conclusion that a site is uncontaminated. It can support a conclusion that further investigation is or is not warranted, and it can define where the intrusive work should go. The distinction between Phase 1 and Phase 2 land contamination work turns on exactly that, and the question of what triggers the dig is answered by the conceptual model the desk study produces.

Presenting the sequence in a desk study

Put the map review in a table rather than in prose, with one row per edition and the columns listed above. Reproduce extracts at a legible scale with the site boundary overlaid and a north arrow, and label each with its survey and revision dates rather than only the publication year.

Then draw the conclusion explicitly. Which potential sources the map history identifies, where they sit relative to the proposed development, and what that means for the source, pathway and receptor linkages you are testing. A reviewer should be able to follow the line from a vanished pond in 1899 to a proposed trial pit location on the exploratory hole plan.

Land contamination reporting is one of the areas where a suitably qualified and experienced person is required. The Environment Agency's land contamination risk management guidance and BS 10175 both assume a competent author, so a Land Contamination Assessment drafted with AI assistance is a starting point for that professional rather than a substitute for them, and the note on suitably qualified persons for land contamination reports sets out what councils look for.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified contaminated land specialist before relying on it.

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