Practical guides
Step-by-step material for working with coordinates in the real world. These articles walk through specific tasks rather than explaining concepts in the abstract. For background theory, see /learn; for the calculator-style utilities, see /tools.
How to
Task-oriented walkthroughs. Each one ends with a worked example using real coordinates.
How to read coordinates
Visual fingerprints and component-by-component decoding rules for the six common formats — DD, DMS, DDM, UTM, MGRS, Plus Codes.
How to write coordinates
Choosing the right format, precision, and convention for CSV, journalism, aviation, search-and-rescue, scientific work, and GeoJSON.
Convert between Decimal Degrees, DMS, and DDM
The conversion math between the three angular formats, with a worked Empire State Building example, precision trade-offs, and the 60-second carry bug.
Why latitude comes first (and when it doesn’t)
The coordinate-order convention. ISO 6709 mandates latitude first; GeoJSON, WKT, PostGIS, and KML mandate longitude first. The 90° detection rule and a parser-boundary pattern.
Sign conventions and sign-loss bugs
Signed numbers vs. hemisphere letters (N/S/E/W); arithmetic conversion both ways; CSV strip, Unicode minus, dual indicators, antimeridian wraparound; the IEEE-754 negative-zero edge case.
Precision versus accuracy in coordinates
NIST’s distinction between recorded resolution and closeness to truth. Four worked accuracy contexts and the 5-decimal rule of thumb for consumer-GPS-derived coordinates.
Decision guides (X versus Y)
Side-by-side comparisons for the choices that come up often when working with coordinates and reference systems.
WGS 84 versus NAD 83
When the 1–2 m horizontal offset between WGS 84 and NAD 83 in CONUS matters — and when it doesn’t.
GPS versus GNSS
GPS is one of five operational global satellite navigation systems. When the distinction matters for accuracy, coverage, and software.
Great circle versus rhumb line
Shortest path versus constant-bearing path. Why pilots favour great circles for long flights and ship navigators historically favoured rhumb lines.
Magnetic north versus true north
The declination angle, the World Magnetic Model, and when navigators need to convert between the two references.
Elevation, altitude, and ellipsoidal height
Three terms that mean different things. Mean-sea-level reference (geoid), ellipsoid reference, and the geoid-ellipsoid separation.
Forward versus reverse geocoding
Address → coordinates versus coordinates → address. Confidence levels, accuracy classes, and when each direction is the right tool.
Tool-paired walkthroughs
Every tool page on /tools includes a “How to use” section, worked examples, and an evergreen explainer for the formula behind the calculation. The tool itself is the fastest route to an answer; the surrounding prose is the guide.