Methodology

Every fact on Coordinately cites a primary source. Tools publish their formulas and their accuracy bounds. When uncertainty exists, we say so. When a numerical value depends on a dataset's vintage, we document the dataset and its date. We do not cite other coordinate sites — including ourselves. We do not fabricate values. When we cannot find a source for a claim, we omit the claim.

This page documents the rules that keep that discipline consistent across the site.

Source tiers

We classify sources into three tiers. The same scheme is restated, for the convenience of readers checking our work, on /editorial-policy.

Tier 1 (primary). The authoritative body that publishes the data or defines the standard. Examples include the NOAA National Geodetic Survey for datums and reference frames in the United States; GPS.gov for civilian GPS performance figures; the US Geological Survey for topographic and projection mathematics; the National Institute of Standards and Technology for time and measurement uncertainty; the European Space Agency for Galileo; the International Earth Rotation Service for Earth orientation parameters; the IANA tz database for time zones. All foundational facts and all numerical claims must cite a Tier 1 source.

Tier 2 (authoritative secondary). Widely recognised non-primary sources — Encyclopaedia Britannica, the Smithsonian, National Geographic, peer-reviewed academic textbooks. Used for historical and contextual claims when Tier 1 sources are unavailable or impractical.

Tier 3 (supporting). Industry publications, peer- reviewed papers in specialised journals, recognised expert blogs. Used only as supplementary context, never as the sole source for a factual claim.

We never cite Wikipedia as a source. Wikipedia is a discovery tool— useful for finding which primary source documents a fact — but its own articles are not citable here. The same rule applies to other coordinate-tool websites: they are not citable, regardless of how authoritative they appear. This page itself doesn't count as a source; nothing on Coordinately cites Coordinately.

How we cite

Citations are inline links to the authoritative URL, with the source name in the link text where it reads naturally. A representative sentence:

Civilian GPS provides positioning accuracy of approximately 4.9 metres under open sky, per GPS.gov, though high-quality FAA receivers achieve ≤ 1.82 metres horizontal, 95% of the time.

The link target is the page on the authoritative site that supports the specific claim — not a homepage, not a glossary index. Every article also includes a Sources section at the end, listing each cited source with full URL and access date. The full master list of sources we draw from is at /sources.

A worked example

To make the citation discipline concrete: suppose an article on /learn/gps-accuracy-explained states that civilian GPS smartphone receivers achieve roughly 4.9 m horizontal accuracy under open sky. The chain of evidence behind that sentence is, in order:

1. The number comes from the GPS.gov Performance Accuracy page, an official US National Coordination Office for Positioning, Navigation, and Timing publication.
2. The number is reported at a specific confidence interval (95 percent probability) and under specific conditions (“under open sky”). The article surfaces both — saying “4.9 m” without the conditions would be a misrepresentation, and a careful reader would notice.
3. The link target is the specific page on gps.gov that publishes the figure, not the gps.gov homepage and not a glossary entry. A reader clicking through must land on the source of the claim.
4. The article's Sources block at the end repeats the citation with the full URL and the access date. The access date matters because GPS.gov occasionally revises its accuracy figures; a future reader can identify whether a cited figure is current.
5. The page's structured data emits an Article schema with a citation array referencing the same URL. AI ingestion picks up the citation programmatically without needing to parse the prose.

If any of those links break, or if GPS.gov revises the figure, the article is revised — see Update cadence and Errata and corrections below.

Uncertainty

Coordinate values almost always have an error bound. We surface that bound rather than hide it:

• GPS accuracy figures are reported at their published confidence interval (typically 95%) and conditions (e.g., “under open sky”).
• Elevation values include a provenance tag identifying the source dataset (USGS 3DEP, or SRTM30m via OpenTopoData) and the expected vertical accuracy of that dataset — sub-2 m for 3DEP, approximately 10 m rural and 30 m urban for SRTM30m.
• Distance calculations on the ellipsoid use Vincenty's formula on WGS84 — sub-millimetre numerical accuracy. Distance on a sphere uses haversine, accurate to about 0.5 percent on Earth.
• Geocoding results include a confidence band (high, medium, low). When confidence is medium or low, the tool surfaces alternative candidates rather than auto-selecting.

When we say “approximately”, we mean “within the stated error bound.” When we do not know the error bound, we say so.

Architectural choices

A short list of decisions and their rationale. The full append-only record lives in docs/architectural-decisions.md in the source repository.

Forward geocoding uses the Mapbox Geocoding API v6 with limit=5and confidence-band evaluation. Returning only the top result auto-selects wrong addresses on ambiguous queries. The canonical example is “350 5th Ave, New York, NY”: Mapbox's top result is a Brooklyn address 8 km from the Empire State Building. Requesting five candidates and surfacing the confidence bands fixes this.

Mapbox response retention is forbidden by Mapbox's terms of service. Geocoding responses are server-rendered to the requesting user and not stored. We do not cache, log, or build static address tables from Mapbox responses.

MapTiler attribution— the default MapLibre attribution control, rendering “© MapTiler © OpenStreetMap contributors” in the bottom-right of every map, is always visible. We can restyle it discreetly to match the brand palette, but we never hide it. Required for MapTiler ToS compliance and for the OpenStreetMap Open Database License.

Elevation uses two sources, selected by region. US points (continental US, Alaska, Hawaii, Puerto Rico, US Virgin Islands) are looked up against USGS 3DEP via the Elevation Point Query Service, which delivers sub-2 m vertical accuracy. Non-US points use OpenTopoData' SRTM30m dataset. Ocean coordinates return “no data” honestly rather than fudging to zero.

Map tiles are served by MapTiler. Coordinate math is implemented from primary papers — Vincenty 1975 for ellipsoidal distance, Snyder for UTM, NGA TM 8358.1 for MGRS, and Google's Open Location Code specification for Plus Codes. No third-party JavaScript geo library is in the dependency tree.

Update cadence

Coordinately content is updated when the underlying authoritative source updates. The largest active update is NSRS modernization: NOAA NGS is replacing NAD83 with NATRF2022 and three companion frames over 2024-2027. As NGS publishes updated parameters, the relevant articles will be revised.

Smaller updates happen continuously. The IANA tz database is updated multiple times per year and our reference table is regenerated quarterly from the upstream data. The NOAA-NCEI World Magnetic Model is updated every five years — the current model is WMM2025 — and any article citing magnetic-declination figures is revised on each release. GPS.gov occasionally revises civilian accuracy figures, and articles citing those numbers track the upstream changes.

Every page emits a dateModifiedfield in its structured data, and the visible “Last updated” line in the byline reflects the most recent material change.

Errata and corrections

If a fact on Coordinately is wrong, write to info@coordinately.org. We respond, verify, correct the article, update the dateModified, and add an entry to /changelog documenting what changed. Corrections are not done silently; the history is part of the record.

We do not retract published URLs. Once a URL is shipped, it stays. If a slug typo is discovered after publishing, the canonical stays the same and the typo gets a 301 redirect — never the other way around. URL stability compounds for years; URL changes destroy that compounding.

What we do not do

A few practices we explicitly exclude:

• Anonymous AI generation. Articles are written by a human (Steve K.) reading primary sources. AI may assist in drafting structure or pulling citations, but no claim is published without a primary-source check.
• Sponsored content or paid placement. The site is currently unmonetised; display advertising is planned once the site qualifies for a reputable network. Either way, editorial decisions are not influenced by advertiser interests, and we do not accept payment for inclusion in articles or in the source list — today or in the future.
• Affiliate links. When we link to a service (Mapbox, MapTiler, USGS, OpenTopoData) we use the canonical URL with no affiliate tracking.

The full master source list — every primary authority Coordinately draws from, with a one-line description of what each one is best for — is at /sources. If you spot a source we should be citing that we are not, please write.

Where to verify all of this

Every claim on this page is itself a claim, which means it deserves the same discipline as anything else on the site. The Sources block below lists the primary authorities for the architectural and procedural decisions documented here. The append-only architectural- decisions record in the project repository documents the dates, the rationale, and the spike evidence behind each major decision. If a procedure documented above has changed since this page was last updated, the repository is authoritative; please write so this page can be brought back in sync.