Database Systems Research Papers - Academia.edu (original) (raw)

1. Location, shape, size and orientation are potentially relevant characteristics of geographic objects. Try to provide an application example in which these characteristics do make sense for (a) point objects, (b) line objects, (c) area objects. 2.To distinguish with examples, the raster-based and vector-based representations of geographic phenomena and Discuss the advantages and disadvantages of each. The following is the difference between the raster based and vector based representation of geographical phenomena: In raster data, the cell typically represents the predominant phenomena of the area covered by a cell, whereas vector data can accurately delineate or identify individual features. As a result, when representing geographic features in a raster dataset, features become collections of cells with the same attribute values but lose their unique identities. Raster data is best used when a primary concern is with the locational relationships of the phenomena represented by geographic features, not the features themselves. Examples of raster data includes thematic data (also known as discrete), representing features such as land-use or soils data, Continuous data, representing phenomena such as temperature, elevation or spectral data such as satellite images and aerial photographs and Pictures, such as scanned maps or drawings and building photographs Examples of vector data includes individual points, country boundaries, and dots which (for 2D data) are stored as pairs of (x, y) coordinates. The points may be joined in a particular order to create lines, or joined into closed rings to create polygons, but all vector data fundamentally consists of lists of coordinates that define vertices, together with rules to determine whether and how those vertices are joined. Below are set of discussed advantages and disadvantages of each. Vector Data Advantages: Data can be represented at its original resolution and form without generalization. Graphic output is usually more aesthetically pleasing (traditional cartographic representation); Since most data, e.g. hard copy maps, is in vector form no data conversion is required. Accurate geographic location of data is maintained. Allows for efficient encoding of topology, and as a result more efficient operations that require topological information, e.g. proximity, network analysis. Disadvantages: The location of each vertex needs to be stored explicitly. For effective analysis, vector data must be converted into a topological structure. This is often processing intensive and usually requires extensive data cleaning. As well, topology is static, and any updating or editing of the vector data requires rebuilding of the topology. Algorithms for manipulative and analysis functions are complex and may be processing intensive. Often, this inherently limits the functionality for large data sets, e.g. a large number of features. Continuous data, such as