Vector and Raster Data Example 

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... data that represented in GIS are in term of raster format and point. The structure of spatial data explains that graphic data represented at the physical level are arranged in one of two methods for a GIS: raster and vector . Data in raster format are stored in a two-dimensional matrix of uniform grid cells (pixels). The major disadvantage of pixels is the volume of data they create. Using raster data is therefore suited to computers with fast coprocessors and fast graphic processing cards. Data in vector format are objects represented by strings of co-ordinates. A point is held as one co-ordinate; a line is held as a number of co-ordinates along its length; the more co-ordinates the greater the accuracy of representation; a polygon is held as a set of co-ordinates at its corners. Raster has many advantages over vector: it is easy to capture data, and area/polygon analysis and combining data layers are far more advanced than vector. On the other hand, vector has advantages over raster in the following areas: linear network analysis, geometrical accuracy, and it have small data volumes. Figure 1 represented Raster and vector data structure of spatial data [7]. The common requirement to access data on the basis of one or more classes has resulted in several GIS employing organizational schemes in which all data of a particular level of classification, such as roads, rivers or vegetation types are grouped into so called layers or overages. The concept of layers is to be found in both vector and raster models. The layers can be combined with each other in various ways to create new layers that are a function of the individual ones. The characteristic of each layer within a layer-based GIS is that all locations with each layer may be said to belong to a single Arial region or cell, whether it be a polygon bounded by lines in vector system, or a grid cell in a Raster system. But it is possible for each region to have multiple attributes. The Figure 2 shows layers and coverage concept in GIS [8]. Spatial database is a database that stores spatial objects and manipulates spatial objects just like other objects in the database. On the other hand, spatial data is the data which describes either location or shape and these objects can be viewed as points, lines and polygons. For examples, roads are represented as lines, mail boxes are represented as point and land use classifications are represented as polygons. Spatial relationships are not just interested in location but are also interested in relationships between objects that are very hard to model outside the spatial domain. The common relationships are proximity (distance), adjacency (“touching” and “connectivity”) and containment (inside/overlapping). For instance, the distance between a toxic waste dump and a piece of property you were considering buying [9]. It has been proposed that in various fields there is a need to manage geometric, geographic, or spatial data, which means data related to space. The space of interest can be, for example, the two-dimensional abstraction of (parts of) the surface of the earth that is, geographic space, a volume layout of a VLSI design or a volume containing a model of the human brain, or three-dimensional space representing the arrangement of chains of protein molecules. The term “spatial database system” has become popular during the last few years, to some extent through the series of conferences “Symposium on Large Spatial Databases (SSD)” held bi-annually since 1989, and is associated with a view of a database as containing sets of objects in space rather than images or pictures of a space. Indeed, the requirements and techniques for dealing with objects in space that have identity and well- defined extents, locations, and relationships are rather different from those for dealing with raster images [10]. Spatial database is the storage of geographical data in prescribed format, including the location shape and description of geographical features as well as the relationships between different features. A spatial database usually includes coordinates and topological information ...