Geography Reference
In-Depth Information
Local Coordinate Systems
A system like the PLS is registered to a meridian and a baseline that have
known coordinate values. Further, any PLS locations can be associated with
other coordinate systems. While it is possible to determine coordinate loca-
tions in the PLS, the system functions without any reference to coordinates
associated with the earth's size or shape.
Local systems are further removed from relationships with the earth's
size or surface. Although the Roman centuration relied on meridians, which
were surveyed based on astronomical observations and measurements, the
survey of PLS meridians makes the relationship with the earth's size and sur-
face and with other meridians secondary, meaning for surveying and legal
purposes that a portion of the PLS is essentially a local location system.
Smaller local coordinate systems are very commonplace because they are
very handy for quickly aiding people to use and orientate themselves with
maps. However, they are of no use for recording the location of things and
events when they should be used with other locational and coordinate sys-
tems.
RECTANGULAR COORDINATE SYSTEMS
Rectangular coordinate systems are different from locational systems in that
they are associated with a particular model of the earth's size and shape
(geoid or ellipsoid). A datum is usually also associated with a particular pro-
jection. However, this broader use of the term has become more common-
place.
The PLS system, when associated with a rectangular coordinate system,
Figure showing an arbitrary local locational system for Minnesota highways and
towns.
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