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In theory, either the vector or the raster format can be used to
represent features in a GIS. In practice, however, one format is more
suitable for certain operations. For example, it is easier to compute the
length of a vector line, but it is easier to determine whether two areas
overlap when they are in raster form.
In order to make the best use of the two formats, we might want to convert data from vector format to raster. There is also a need for the reverse conversion from raster to vector, although this conversion is much more complicated. We will describe the conversion of vector polygons to raster zones. As explained in the chapter on Overlay Analysis, zones are composed of pixels with similar attributes and could be used in overlay analysis. They are different from raster images, which can only be used as backdrops.
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Make a zone out of a polygon.
Calculate the area of the zone.
For a raster representation, the area is computed simply by counting the number of pixels and multiplying the result with the area of a pixel, which is one square metre in this case. |
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