Why Is it Helpful to Have a Grid on a Map?
Maps are graphical devices intended to convey detailed and accurate spatial data. Modern map making is a combination of geography, cartography, statistics and effective visual communication strategies. Maps designed to cover vast areas in significant detail will commonly overlay the data with a grid reference.
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Alphanumeric Cells
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Street and city maps often use a simple alphanumeric grid, or atlas grid. An atlas grid is a simple coordinate system which references each cell by the combination of numbers and letters. One axis uses letters, while the second axis uses numbers. A typical atlas grid implementation will list each and every point of interest found on the map, organized by cell. A user looking for a specific point on a map will be able to quickly narrow their search to a single grid cell.
Cartesian Coordinates
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A map using a Cartesian coordinate system will use numbers along both axes. Rather than referring to an entire cell, Cartesian coordinates are specific to a single point. René Descartes, a 17th century French mathematician, developed analytic geometry and the Cartesian coordinate system. This breakthrough in geometry and algebra permitted users and map makers to perform operations between sets of coordinates. Simple formulas are used to calculate distances between points, degrees of angles and vectors, curve arc length and other desired geometry. All modern geocoordinate systems and geospatial statistical methods are built upon the foundations of Cartesian coordinate theory.
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Nested Grids for Precision Coordinates
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A map using a grid coordinate system can break individual cells down into smaller grids, increasing the precision of coordinates. By superimposing a new 10x10 grid within a cell, numbered from zero to nine along each axis, a map user gains additional coordinates to refer to.
Military Grid Reference System
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The MGRS is a modern military coordinate system standardized for use by NATO militaries. The system was developed by combining the Universal Transverse Mercator (UTM) coordinate system and the Universal Polar Stereographic (UPS) grid. The Military Grid Reference System uses the intersection of numbered UTM zones and lettered latitude bands to form a "Grid-zone designation." The Grid-zone designation (GZD) is further broken down into 100,000 meter square identifiers, referenced by letters on each axis. Each square identifier is then reduced in multiples of 10 until reaching a unit size of one meter squared.
MGRS Precision Coordinates Example
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13S (Grid Zone Designation)
13SED -- A point within a 100,000 meter square
13SED01 -- A point within a 10,000 meter square
13SED0917 -- A point within a 1,000 meter square
13SED095177 -- A point within a 100 meter square
13SED09501770 -- A point within a 10 meter square
13SED0950217703 -- A point within a 1 meter square
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References
- Photo Credit world map image by Andrew Brown from Fotolia.com
