Vector And Raster Data In Gis Computer Research Essay

A Geographical Information System (GIS) is a way of spatially holding, analysing, manipulating, taking care of and displaying physical data. GIS data represents real items such as roads, rivers, urban areas, place labels, railway, tourist destinations, town labels etc. with digital data deciding the combination. A geodatabase is a databases that is in some way referenced to locations on earth. Customarily, there are two wide methods used to store data in a GIS; raster images and vector. Ordnance Review Ireland (OSI) data is supplied in both Vector and Raster format. In both cases the data is geo-referenced.

VECTOR AND RASTER DATA

Vector data is split into three types; polygon, lines (or arc) and point data. Vector is a way for saving spatial data affecting assigning coordinates for every entity; an X, Y, Z for a point, a set of such things for a range and a series of such lines for a polygon. This technique is very helpful for modeling discrete physical features.

Different physical features are indicated by different kinds of geometry

Points

A point is a zero-dimensional abstraction of any object symbolized by a single X, Y co-ordinate. It is normally used to symbolize a geographic feature too small to be exhibited as a range or a location (e. g. location of any building on a little range map or, for example, cities over a map of the world might be symbolized by tips not polygons). No measurements are possible with point features.

Figure 1- Vector representation

Source: http://www. geom. unimelb. edu. au/gisweb/GISModule/GIST_Vector. html

Lines or polylines

A group of co-ordinates that signify the form of geographic features that are too narrow to be exhibited as a location, such as, region boundary lines or contours. At small scales geographic features may have no area, e. g. streams or streets and may be displayed as linear features somewhat than as a polygon. Series features can evaluate distance.

Polygons

Polygons are used to signify areas. Such as for example lakes, park boundaries or land uses etc. Polygons convey the most amount of information of the document types and can assess perimeter and area.

Rigaux et al. (2002:p. 38) areas, 'A point is represented by its couple of coordinates, whereas more complex linear and surfacic things are represented by buildings (lists, models, arrays) on the idea representation. ' These geometries can be linked to a row in a repository that represents their attributes. For instance, a database that details lakes may include a lake's depth, drinking water quality, pollution level. Different geometries can even be likened and the GIS could be used, for example, to identify all wells (point geometry) that are within one kilometre of any lake (polygon geometry) that has a higher level of pollution. Vector data can be displayed at any level and individual tiers (e. g. highways, complexes, etc) can be exhibited or omitted (see Appendix A).

Raster

Ellis states 'that raster is a method for the safe-keeping, processing and display of spatial data. ' There are three types of raster datasets; thematic data, spectral data and pictures. Raster data consists of rows and columns of skin cells, with each cell holding a single value. Raster data can be images containing specific dots with coloring values, called cells (or pixels), assemble in a rectangular equally spaced array.

'Each cell must be rectangular in shape, but not necessarily square' (Ellis 2001). Each cell within this matrix includes location co-ordinates as well as an attribute value. The spatial location of every cell is implicitly comprised within the purchasing of the matrix, unlike a vector composition which stores topology explicitly. Areas filled with the same feature value are accepted as such, however, raster constructions cannot identify the limitations of areas such as polygons.

Raster data can be an abstraction of the real world where spatial data is expressed as a matrix of cells or pixels with spatial position implicit in the ordering of the pixels. Using the raster data model, spatial data is not continuous but split into discrete products. Ellis areas that 'this makes raster data specifically suitable for certain types of spatial operation, for example overlays or area calculations. '

Raster structures may lead to increased storage using situations, since they store each c