Raster data is a grid of cells covering an area of interest. Each pixel, the smallest unit of information in the grid, displays a unique attribute.
An example of raster data is a scanned image or photograph. A line drawn in a raster format must be defined by a group of pixels along the length of the line. As a result the size of a raster file is larger than that required by a vector file.
raster representation of data
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Raster is a method for the storage, processing and display of spatial data. Each area is divided into rows and columns, which form a regular grid structure. Each cell must be rectangular in shape, but not necessarily square. Each cell within this matrix contains location co-ordinates as well as an attribute value. The spatial location of each cell is implicitly contained within the ordering of the matrix, unlike a vector structure which stores topology explicitly. Areas containing the same attribute value are recognised as such, however, raster structures cannot identify the boundaries of such areas as polygons
rasterisation of vector data
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The process of converting vector data, which is a series of points, lines and polygons, into raster data, which is a series of cells each with a discrete value. This process is essentially easier than the reverse process, which is converting data from raster format to vector format.
raster to vector conversion
The process of converting an image made up of raster cells into one described by vector data. This may or may not involve the encoding of topology.
