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Maps GPS Glossary - M

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magnetic declination - The difference, in degrees, between magnetic north and true north.

magnetic north - A point on the earth about 500 miles from the north pole toward Hudson Bay in Canada; this is where a compass points. In the U.S., magnetic north can vary up to approximately 22 degrees from true north.

magnetic variation - Same as magnetic declination.

maidenhead grid squares - A system designed to facilitate the designation of geographical positions for use within the amateur radio community.

map projection - The method used to convert the spherical shape of the earth onto the plane of a map.

map projection deformation - The error or distortion that results when the spherical shape of the earth is projected onto the plane of a map.

mask angle - The minimum acceptable satellite elevation above the horizon to avoid blockage of line-of-sight.

MCX - A type of GPS antenna connection.

mean sea level - The average height of the sea surface, based upon hourly observation of the tide height on the open coast or in adjacent waters that have free access to the sea. In the United States, it is defined as the average height of the sea surface for all stages of the tide over a nineteen year period. Mean sea level, commonly abbreviated as MSL and referred to simply as 'sea level,' serves as the reference surface for all altitudes in upper atmospheric studies.

Mercator projection - A cylindrical map projection devised by Gerardus Mercator in 1569. Its parallels and meridians are straight lines, and the unavoidable east-west stretching away from the equator is accompanied by a corresponding north-south stretching, so that at each location the east-west scale is the same as the north-south-scale.

meridian - An imaginary line circling the earth, passing through the north and south poles; a line of longitude.

MGRS - Military Grid Reference System. A metric grid system that is a subset of the UTM system. It uses letter pairs to represent 10km squares.

microstrip antenna - A GPS antenna constructed of one or more elements that are photoetched on one side of double-coated, printed-circuit board.

minute - A unit of measurement; one degree contains 60 minutes.

MOB - Man Overboard - A GPS receiver function that allows marking a specific location so that you can return to that location at a later time.

monadnock - An isolated rocky mass or ridge that stands isolated in a gently sloping area. It is also known as inselberg.

moraine - Stones, boulders, and other debris deposited by a glacier.

morrow - A rounded hill.

moving map - A program that displays your position in real time on the top of either a Vector or Raster map using GPS input.

MSAS - MTSAT Satellite-based Augmentation System - Japanese version of WAAS - covers parts of Asia and the Pacific

MTSAT - Multi-functional Transport Satellite - A satellite with two main functions: a meteorological mission conducted by Japan Meteorological Agency; an aeronautical mission conducted by Japan Civil Aviation Bureau of the Ministry of Land, Infrastructure and Transport of Japan (MLIT).

multi-channel receiver - A GPS receiver that can simultaneously track more than one satellite signal.

multipath - Interference caused by reflected GPS signals arriving at the receiver, typically as a result of nearby structures or other reflective surfaces.

multipath error - An error caused by the interference of a signal that has reached the receiver antenna by two or more different paths. This is usually caused by one path being bounced or reflected.

multiplexing receiver - A receiver capable of switching very fast between satellites being tracked.


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