For example, a DEM has 1 band, whereas a aerial photo in color may have 3 bands. A raster dataset may be composed of one or more bands. If the display scale of two images is the same/similar, but the cell size differs, the image with the smaller cell size will display greater detail and appear to provide a more thorough conclusion. An example of this is a display scale of 1:10,000 has less detail than a display scale of 1:5000. Scale refers to the level of detail displayed. The spatial resolution required depends on the type and scale of analysis, accuracy of the study and limitations such as time and data size. Spatial resolution refers to the cell size and determines the level of detail that will be included within the raster display. Raster data is composed of cells in a grid like structure. Raster data can be stored in various formats including DEM's (Digital Elevation Models), USGS, ESRI Grids, and image formats including JPEG, TIFF, IMG and GIF. Rasters can also be digital or scanned documents that can be used as attributes of a feature collected from a variety of sources such as aerial photography, satellite sensors, scanning maps, surveying, and from converting vector to raster data. Raster data tends to typically provide greater details, has a larger data volume and allows for more advanced analyses than vector data. These data models complement each other but can be converted if necessary using various conversion tools. Vector models serve as the other primary dataset used in ArcGIS. Vector data modelsrepresent discrete points, line and polygons that are not continuous in nature. The smaller the cell size, the greater the resolution and file size of the raster. temperature, elevation, land-use, soil type). Raster vs vectorīoth types of data are very useful, but there are important differences.Problem: Conversion techniques of vector data to raster data.Īnalysis Procedures: Raster data is a field based data model that represents geography as a continuum though using grid cells that store attribute values, but can also be used as discrete thematic rasters (i.e. The vector version can also store additional context information about these features – the attributes – a very important aspect. To reproduce the building in a GIS the computer reads these values and draws a line linking the coordinate positions. The position and shape of a building is captured as a series of four pairs of numerical coordinates. An area is defined in a similar way, only with the first and last points joined to make a complete enclosure.A line is defined by a sequence of coordinate pairs defining the points through which the line is drawn.A point is defined by a single pair of coordinate values. The features are recorded one by one, with shape being defined by the numerical values of the pairs of xy coordinates, so that: Vector data can be thought of as a list of values. To reproduce the image the computer reads each of these cell values one by one and applies them to the pixels on the screen. The major use of raster data involves storing map information as digital images, in which the cell values relate to the pixel colours of the image. A value is stored in each of these cells to represent the nature of whatever is present at the corresponding location on the ground. The entire area of the map is subdivided into a grid of tiny cells, or pixels. Raster data can be thought of as being similar to a digital photograph. These numerical values can be used to translate map information into digital form, in both vector and raster formats. All locations and shapes can be defined in terms of x and y coordinates from a given grid system. These numbers refer to coordinates from the British National Grid. Look at Ordnance Survey (OS) paper maps and you will notice, along the sides, there are a series of numbers associated with a grid covering the whole map area. These coordinate systems can be local, national or international. Coincidentally maps reference geographical locations on the earth's surface through a system of coordinates. Computers store information in sequences of binary digits (bits), which form a code for every possible number or letter.
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