Rasterization

Rasterization, to convert vector data sets to raster data, involves assigning point, line and polygon attribute values to raster cells that overlap with the respective point, line or polygon. To avoid information loss, the raster resolution should be carefully chosen on the basis of the geometric resolution. A cell size that is too large may result in cells that cover parts of multiple vector features, and then ambiguity arises as to what value to assign to the cell. If, on the other hand, the cell size is too small, the file size of the raster may increase significantly.

Rasterization itself could be seen as a “backwards step”: firstly, raster boundaries are only an approximation of the objects’ original boundary. Secondly, the original “objects” can no longer be treated as such, as they have lost their topological properties. Rasterization is often done because it facilitates easier combination with other data sources that are also in raster formats, and/or because there are several analytical techniques that are easier to perform on raster data. An alternative to rasterization is to not perform it during the data preparation phase, but to use GIS rasterization functions “on the fly”, i.e. when the computations call for it. This allows the vector data to be kept and raster data to be generated from them when needed. Obviously, the issue of performance trade-offs must be looked into.