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An alphanumeric grid (also known as atlas grid [1]) is a simple coordinate system on a grid in which each cell is identified by a combination of a letter and a number. [2]An advantage over numeric coordinates such as easting and northing, which use two numbers instead of a number and a letter to refer to a grid cell, is that there can be no confusion over which coordinate refers to which ...
The World Geographic Reference System (GEOREF) is a geocode, a grid-based method of specifying locations on the surface of the Earth. GEOREF is essentially based on the geographic system of latitude and longitude , but using a simpler and more flexible notation .
Graphical view of the affine transformation. The registration of an image to a geographic space is essentially the transformation from an input coordinate system (the inherent coordinates of pixels in the images based on row and column number) to an output coordinate system, a spatial reference system of the user's choice, such as the geographic coordinate system or a particular Universal ...
For example, in the "1 Geohash digit grid" illustration of 32 rectangles, above, the spatial region of the code e (rectangle of greyish blue circle at position 4,3) is preserved with prefix e in the "2 digit grid" of 1024 rectangles (scale showing em and greyish green to blue circles at grid).
The extra two digits describe a position within the 1-kilometre square. Imagine (or draw or superimpose a Romer) a further 10x10 grid within the current grid square. Any of the 100 squares in the superimposed 10×10 grid can be accurately described using a digit from 0 to 9 (with 0 0 being the bottom left square and 9 9 being the top right square).
A grid-based spatial index has the advantage that the structure of the index can be created first, and data added on an ongoing basis without requiring any change to the index structure; indeed, if a common grid is used by disparate data collecting and indexing activities, such indices can easily be merged from a variety of sources.
Strabo, in his Geography (ca 20 AD), states that the maps in Eratosthenes's Geography Book 3 (3rd century BC, now lost) contained lines "drawn from west to east, parallel to the equatorial line" (thus the term parallel) [6] Ptolemy's Geography (ca 150 AD) gives detailed instructions for drawing the parallels and meridians for his two projections.
For example, Albany, New York is roughly 140 miles north of New York City. Every site on Earth has a unique absolute location, which can be identified with a reference grid (such as latitude and longitude). Maps and globes can be used to find location and can also be used to convey other types of geographical information.