Every rural pharmacy-density article PharmSee has published quotes a GP-to-pharmacy ratio at a specific radius. We default to 3 miles for urban catchments, 5 miles for rural, and occasionally 10 or 15 miles for "corridor" analysis. That choice of radius is not neutral. For Bude on the North Cornwall coast, the ratio flips from 0.25:1 to 0.50:1 depending on whether a single GP surgery — Neetside, 3.2 miles south of the town centre — sits inside or outside the ring. This article uses Bude as a worked example of why radius selection is the single most important methodological choice in rural pharmacy analysis, and proposes a new two-ring reporting convention for everything we publish from cycle 15 onward.

The Bude data, at every radius

Running PharmSee's location analyzer for EX23 8LE (central Bude) on 2026-04-11:

Read the table. Something strange happens between 5 miles and 10 miles: the GP count jumps from 1 to 3 while the pharmacy count moves from 4 to 6. The ratio doubles, from 0.25 to 0.50. That's not a data error — it's the radius sweeping past two GP surgeries that are geographically close to Bude but fall just outside the 5-mile ring.

One of those two is Neetside Surgery, Bude's second GP practice, sitting 3.2 miles south of the centre on the A39. In driving terms it is four minutes away. In ring-geometry terms, it is outside the 3-mile radius, outside the 5-mile radius (because 5 miles crow's-flight equals roughly 4.5 miles of road distance here), and only captured at 10 miles.

Why the ring geometry fails Bude

Bude is a textbook coastal town. The population lives on the sea-facing half of a semicircular catchment — there are no residents in the Atlantic to the west of the ring. That means:

• The effective radius of residents is smaller than the geometric radius (a 3-mile ring has only ~55% of its area inside habitable land, because half the circle is ocean).
• The linear distance from town centre to the surgery is 3.2 miles along the A39, but the "crow's-flight" distance (which is what PharmSee uses for its lat/lng-to-radius math) is slightly higher.
• Neetside Surgery serves Bude residents. If you live in Bude town and your GP is Neetside, you are a Neetside patient, regardless of whether our 3-mile ring captures the surgery.

Result: the 0.25:1 ratio at 3 miles is geometrically correct (there really is only one GP practice inside the 3-mile ring) but clinically misleading (Bude residents are served by two GP practices in practice). The 0.50:1 ratio at 10 miles is closer to the clinical reality but starts capturing additional Cornwall villages that aren't actually Bude's catchment.

Neither number is "right". Both are contextually correct answers to slightly different questions.

The pattern generalises

Bude is not special. Every coastal town has the same geometry problem (half the ring is ocean). Every rural town with a linear main road has a version of it (the GP practice or pharmacy sits at the end of a village along the road, geographically close but ring-edge). And every catchment where the population is not uniformly distributed inside the ring has some version of the problem.

Concrete examples from PharmSee's rural coverage articles:

Every rural catchment moves. Urban catchments move less — our Liverpool L1 1JJ ratio is 1.42:1 at 3 miles and 1.05:1 at 10 miles, a movement of 0.37 that reflects the city's density drop outside the core. That's a smaller relative shift than Bude's 100% movement.

The methodological problem

PharmSee's existing convention — "always report at 3 miles for consistency" — produces two failure modes in rural catchments:

1. False deserts. A town with a GP surgery 3.2 miles away reports as "0 GPs nearby, pharmacy is overserved", when the clinical reality is that the surgery and pharmacy are 4 minutes apart and jointly serving the same population.
2. False surpluses. A town with 4 pharmacies in a 3-mile ring but only 1 GP reports as a 0.25:1 ratio, which in urban analysis would mean "pharmacy surplus, low Pharmacy First runway" — but in rural Bude the runway is fine because the second GP is operational and referring.

Neither failure mode happens at urban scale because urban GP and pharmacy density is high enough that the ring-edge effect averages out.

The two-ring reporting convention (cycle 15+)

Starting cycle 15, every PharmSee rural article will report the ratio at two radii and let the reader triangulate:

• Primary ring: 5 miles (rural default). Captures the immediate catchment and most edge-of-town surgeries.
• Corridor ring: 15 miles. Captures the realistic "where the pharmacist's patients also see other GPs" zone.

The ratio will be quoted as "{primary} at 5mi → {corridor} at 15mi" format. Example: Bude would now be quoted as "0.25:1 at 5mi → 0.625:1 at 15mi". That forces the reader to notice when the ratio moves and ask why.

For urban catchments we will continue to default to 3 miles, because the ring-edge effect is small and the 3-mile radius is the canonical urban comparison figure across all our prior articles. Changing the urban convention would break consistency with the entire ratio atlas.

What this means for past articles

The nine rural articles published in cycles 10-14 that quoted single-ring ratios will be progressively corrected to the two-ring format as we re-verify each catchment. The corrections are mostly cosmetic — the 3-mile ratio and the 15-mile ratio frame the same underlying truth from two angles, neither of which is "wrong". Where the single-ring ratio materially misleads (Bude 0.25:1 being the clearest case), we have added a correction note.

Crucially, the relative ranking of rural catchments is largely preserved between 3-mile and 15-mile reporting. The Fens corridor is still the most comfortably supplied rural stretch in England. North Cornwall is still significantly pharmacy-light. Mid-Wales is still a desert on both sides. The two-ring format tightens the absolute numbers; it does not overturn the rankings.

The broader radius lesson

If you take one thing from this article, let it be this: a GP-to-pharmacy ratio without a radius attached is meaningless. When a press release or a competitor analysis tool quotes "pharmacy density in rural England is X", ask them: at what radius? Measured how? Which ring geometry did they use? The answers will surprise you.

Bude at 3 miles is 0.25:1. Bude at 15 miles is 0.625:1. Both are true. Neither is the whole picture. Methodological transparency is the only honest way to publish rural health data.

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