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Latitude and longitude: two coordinates, one format

Understand degrees, minutes and hemispheres before reading a position.

4 min read
Manual contents
In this guide
Schematic grid with the Equator horizontal and the zero-degree meridian vertical. A point lies above the Equator and to the right of that meridian; dashed lines identify its latitude and longitude references. This is not a navigation chart or a real position.
Two coordinates, one position

Original schematic illustration. Read the explanation and limitations in the lesson.

insideSailOriginal insideSail artwork — all rights reserved
Enlarge the diagram
Schematic grid with the Equator horizontal and the zero-degree meridian vertical. A point lies above the Equator and to the right of that meridian; dashed lines identify its latitude and longitude references. This is not a navigation chart or a real position.

On a schematic globe, parallels help identify latitude and meridians identify longitude. The grid is not a network of equal-sided squares. The illustration explains the references; it is not a way to measure a voyage.

The decimal point is not decoration

A degree divides into 60 minutes of arc, and a minute into 60 seconds of arc. These are not minutes of time. You may see decimal degrees, degrees with decimal minutes or degrees/minutes/seconds. N and S identify latitude hemispheres; E and W identify longitude hemispheres.

Coordinates have a reference too

Two panels distinguish chart references: the horizontal panel uses a grid and a point to ask where it is; the vertical panel uses a reference line to ask relative to which level. The caption asks readers to check the datum stated on the chart itself. No real depth is shown.
Two kinds of reference

Original schematic illustration. Read the explanation and limitations in the lesson.

insideSailOriginal insideSail artwork — all rights reserved
Enlarge the diagram
Two panels distinguish chart references: the horizontal panel uses a grid and a point to ask where it is; the vertical panel uses a reference line to ask relative to which level. The caption asks readers to check the datum stated on the chart itself. No real depth is shown.

A horizontal reference frames positions; a vertical reference frames heights or depths. They are not the same field. When recording data, retain known format, units and reference. Adding decimal places does not create precision the source never had.

Concepts in this lesson

Latitude

An angular coordinate north or south of the equator.

Longitude

An angular coordinate east or west of the reference meridian.

Sources and references

  1. Cartografia — cartas náuticas ↗

    Instituto Hidrográfico · Live institutional page · Chart information and vertical reference

    Version: Live institutional page. Jurisdiction: Portugal.

    Checked on
  2. What is latitude? ↗

    NOAA National Ocean Service · Parallels, equator, degrees, minutes and seconds

    Version: Institutional page. Jurisdiction: International.

    Checked on
  3. Magnetic declination calculator — coordinate input help ↗

    NOAA NCEI · Coordinate formats; 60 minutes per degree; hemisphere notation

    Version: Institutional page. Jurisdiction: International.

    Checked on

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