Ordnance Survey proved map copying by matching cartographers' habits

Ordnance Survey, Britain's national mapping agency, suspected for years that the Automobile Association was building its road atlases and touring maps by tracing OS survey data rather than surveying independently. The dispute first surfaced in court in 1996 and reached back to allegations dating to 1990, but proving it legally was harder than it looked: a road's location, a village's name, a river's course are facts, and facts are not protected by copyright.

What copyright does protect is the expressive choices a cartographer makes rendering those facts: how a bend in a minor road is smoothed, where a place-name label is nudged to avoid clutter, which symbol conventions are used for a footpath versus a bridleway. OS built its case by comparing its own maps against AA's line by line for exactly these arbitrary stylistic habits — idiosyncrasies with no geographic reason to appear in two independently drawn maps, but every reason to appear if one had simply been traced from the other.

Cross-referenced meaningless cartographic choices—curve smoothing, label offsets—that independent surveyors never match by chance, proving tracing.

Arbitrary choices have no external reference, so independent creators won't converge on them.

Matching these quirks is strong evidence of copying, not coincidence.

The proof is embedded in the product itself, needing no confession or witness.

When your valuable output is unprotectable facts, embed arbitrary stylistic choices; if a competitor reproduces them, you've proven copying.

AA paid OS a £20 million settlement in 2001, after 26 AA maps were found to be direct or substantial copies of OS mapping. Ordnance Survey's fingerprinting method became the standard evidentiary approach across the mapmaking industry for proving copying of factual data that copyright law does not otherwise protect, cited in cartographic infringement cases well beyond Britain.