Grid (spatial Index) - Types of Grids

Types of Grids

"Square" or "rectangular" grids are frequently the simplest in use, i.e. for translating spatial information expressed in Cartesian coordinates (latitude and longitude) into and out of the grid system. Such grids may or may not be aligned with the gridlines of latitude and longitude; for example, Marsden squares, World Meteorological Organization squares, c-squares and others are aligned, while UTM, and various national (=local) grid based systems such as the British national grid reference system are not. In general, these grids fall into two classes, those that are "equal angle", that have cell sizes that are constant in degrees of latitude and longitude but are unequal in area (particularly with varying latitude), or those that are "equal area", that have cell sizes that are constant in distance on the ground (e.g. 100 km, 10 km) but not in degrees of longitude, in particular.

The most influential triangular grid is the "Quaternary Triangular Mesh" or QTM that was developed by Geoffrey Dutton in the early 1980s. It eventually resulted in a thesis entitled "A Hierarchical Coordinate System for Geoprocessing and Cartography" that was published in 1999 (see publications list on Dutton's Spatial Effects website). This grid was also employed as the basis of the rotatable globe that forms part of the Microsoft Encarta product.

For a discussion of Discrete Global Grid Systems featuring hexagonal and other grids (including diamond-shaped), the paper of Sahr et al. (2003) is recommended reading.

In general, triangular and hexagonal grids are constructed so as to better approach the goals of equal-area (or nearly so) plus more seamless coverage across the poles, which tends to be a problem area for square or rectangular grids since in these cases, the cell width diminishes to nothing at the pole and those cells adjacent to the pole then become 3- rather than 4-sided. Criteria for optimal discrete global gridding have been proposed by both Goodchild and Kimerling in which equal area cells are deemed of prime importance.

Quadtrees are a specialised form of grid in which the resolution of the grid is varied according to the nature and/or complexity of the data to be fitted, across the 2-d space, and are considered separately under that heading.

Read more about this topic:  Grid (spatial Index)

Famous quotes containing the words types of, types and/or grids:

    The wider the range of possibilities we offer children, the more intense will be their motivations and the richer their experiences. We must widen the range of topics and goals, the types of situations we offer and their degree of structure, the kinds and combinations of resources and materials, and the possible interactions with things, peers, and adults.
    Loris Malaguzzi (1920–1994)

    He’s one of those know-it-all types that, if you flatter the wig off him, he chatter like a goony bird at mating time.
    —Michael Blankfort. Lewis Milestone. Johnson (Reginald Gardner)

    New York ... is a city of geometric heights, a petrified desert of grids and lattices, an inferno of greenish abstraction under a flat sky, a real Metropolis from which man is absent by his very accumulation.
    Roland Barthes (1915–1980)