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'X' Marks the Spot |
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- Long before the creation of modern day satellite navigation systems
with their highly detailed and interactive mapping
capabilities, we have been documenting geographic
information using the finest tools and methods available at
the time.
- Even maps predating the advent of early cartesian and
geographic coordinate systems were capable of conveying
basic geospatial relationships between significant
landmarks.
- Maps created to record the location of a specific item
often included a dashed line to indicate a suggested path
leading to the desired destination which was frequently
identified with an unmistakable 'X'.
- Today we still use an 'X' to mark important locations in
the form of intersecting coordinates commonly referred to as
latitude and longitude.
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Latitude vs Longitude |
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Latitude |
Longitude |
- Latitude measures distance north or south of the
equator.
- The distance between each degree of latitude is a
constant.
- Geographic shapes and sizes remain consistent from north
to south when comparing most flat maps with a globe.
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- Longitude
measures distance east or west of a prime meridian.
- The distance between each degree of longitude varies
with latitude.
- Geographic shapes and sizes are often distorted from
east to west near the north and south poles when comparing
most flat maps with a globe.
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Latitude on a Globe |
Latitude on a Map |
Longitude on a Globe |
Longitude on a Map |
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Latitude |
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- Latitude is a measurement used to express distance north or south of the equator.
- The
equator is the 0° line of latitude
located halfway between the north and south poles.
- Lines of latitude (also known as
parallels) run east and west, parallel to the
equator, and do not intersect.
- Units of latitude are measured in degrees north or south
of the
equator (0°-90°).
- Locations north of the equator are expressed with a
positive number, or with 'N'.
- Locations south of the equator are expressed with a
negative number, or with 'S'.
- The equator divides the Earth into northern and southern
hemispheres.
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- The
MSL distance between each degree of latitude remains constant at 60 nautical miles (111 km).
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Longitude |
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- Longitude
is a measurement used to express distance east or west of
the prime meridian.
- A
prime meridian is the arbitrary line of
longitude defined as 0° in a geographic coodinate system.
- Lines of longitude (also known as
meridians) run north and south, and intersect each other at the poles.
- Units of longitude are measured in degrees east or west
of the prime meridian (0°-180°).
- Locations east of the prime meridian are expressed as a
positive number, or with 'E'.
- Locations west of the prime meridian are expressed as a
negative number, or with 'W'.
- The line of longitude opposite the prime meridian (180°)
is the
international date line.
- The prime meridian and antimeridian together divide the
Earth into eastern and western hemispheres.
- The
Greenwich meridian is a historic reference line
that passes through Greenwich, London.
- The reference meridian used by the
United States GPS and
WGS84 is the
IRM.
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- The
MSL distance between each degree of longitude is not a
constant, and varies with latitude.
- At the north and south poles (90° latitude), the
distance between each degree of longitude is 0 nm (0 km).
- At 75° latitude, the distance between each degree of
longitude is 15 nm (27 km).
- At 60° latitude, the distance between each degree of
longitude is 30 nm (55 km).
- At 45° latitude, the distance between each degree of
longitude is 42 nm (77 km).
- At 30° latitude, the distance between each degree of
longitude is 52 nm (96 km).
- At 15° latitude, the distance between each degree of
longitude is 58 nm (107 km).
- At the equator (0° latitude), the distance between each
degree of longitude is 60 nm (111 km).
- Tip:
Longitude measurement precision improves as Latitude
values are increased.
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