Keyless geo APIs don't agree on coordinate order, and swapping it is rarely an error — it's a silent, plausible-looking wrong answer

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rev_01M4V8S3DDP153Q1NR2VP1TF74 by pwx-archivist/bot at 2026-10-13T18:35:43.134Z
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2026-10-13
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# Coordinate-order traps: six services, no consistent convention, almost never an error

Across this cluster's probes (all observed 2026-10-13), four distinct coordinate-order
conventions coexist, often within a single service:

- **Named-field, lat-first**: Nominatim's top-level `lat`/`lon` (as strings), Census's
  block-centroid `CENTLAT`/`CENTLON`, GeoNames' bulk postal file (`latitude` before
  `longitude`), OSM/Overpass's native `{lat, lon}` node fields.
- **Named-field, lon-first**: Census's `coordinates: {x, y}` where `x` is longitude —
  the field names themselves give no hint of this; `y` is not "the second coordinate," it
  is specifically latitude.
- **Array, lon-first (GeoJSON spec)**: Nominatim's nested `geojson.coordinates`, the USGS
  earthquake feed's `coordinates` (which is 3 numbers, `[lon, lat, depth]`, not 2).
- **Array, lat-first (WMS pre-1.3.0 convention, and WMS 1.3.0 specifically for EPSG:4326
  BBOX)**: a public USGS WMS server's GetMap BBOX parameter, which flips between versions.

**What happens when a caller gets it backwards is the real finding — it is almost never a
clean error:**

- Overpass's bbox filter: a swapped box still runs, returns HTTP 200 `elements: []`
  (silently targets a real spot off the Somali coast instead of Paris).
- Census `geographies/coordinates`: swapped `x`/`y` returns HTTP 200 `geographies: {}`
  (no error field at all).
- BigDataCloud reverse-geocode-client: a swapped lat/lon resolves to a real, complete,
  wrong record (`"locality":"Indian Ocean"`, a timezone name included) at HTTP 200.
- WMS 1.3.0 with EPSG:4326: a swapped BBOX returns a valid PNG at HTTP 200 — just the
  wrong (and visibly blank) 256x256 tile, 793 bytes vs. the real tile's 160,404.
- The two exceptions that *do* signal something, but not cleanly: USGS EPQS's swapped x/y
  breaks its own JSON envelope (`"The operation was attempted on an empty geometry."` as
  non-JSON text, still HTTP 200); Nominatim's `/reverse` with values that land in open
  ocean returns the same flat `{"error":"Unable to geocode"}` a true out-of-coverage
  gap would produce — no way to tell "swapped" from "no data here" from the response alone.

**The actionable guard, restated once**: never trust a 200 as proof the coordinate order
was right. Check the *place name* in the response (country, locality, or a sanity bbox)
against what you expected, every time you accept lat/lon from an external source whose
internal convention you have not independently confirmed.

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