Geographical Information Systems (Gis)

1. Spatial data are what drive a GIS. Spatial features or entities and their attributes are stored in computers using a number of spatial data models. It is vital to understand the characteristics of them since the data model employed has considerable influence on the functionality of the GIS. Spatial data can represent real world features with discrete boundaries (such as roads, buildings, lakes, rivers, administrative boundaries) as well as real world phenomena with non-discrete boundaries (such as precipitation and nutrient levels, terrain). The basic approaches are: raster data model and vector data model. Depending on the type of problem that needs to be solved, the type of maps that need to be made, and the data source, either raster or vector, or a combination of the two can be used. Each data model has strengths and weaknesses in terms of functionality and representation. | Raster Data Model | Vector Data Model | Descriptions | The raster data model is the simpler model and is based on the division of reality into a regular grid of identically shaped cells. Raster data represent the landscape as a rectangular matrix of square cells.In raster data model, attributes are limited to the numeric values of the cells themselves, and while it is possible to link additional attributes to the groups of cells having same values, which is rarely done in practice because of the low utilizing value and cumbersome data management. | In vector data model, an object’s shape is represented by dots which are located where the shape of the object changes. The dots which are known as vertices are joined by straight lines. Vector data represent features as discrete points, lines, and polygons.In vector model, as a point of difference, vector objects are additionally described by one or more characteristics, in GIS called attributes. Vector files attributes are stored in tables which consists of records (rows) representing individual features, fields (columns) representing a

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