Quad tree decoding also is a way to save space by dividing the grid into four quadrants, saving a reference to the quadrant of the grid only if it contains data. Then the quadrant is split into four half-size quadrants, and so on until the individual pixel is reached. If all the pixels in a quadrant have the same attribute than we only need to store one attribute for all the pixels. Analysis of the radiometric data in raster images can be difficult due to the presence of pixels which may contain data from more than one element. They are commonly called mixed pixels or mixels.
Topology is the property that describes adjacency and connectivity of features.
A topology data structure encodes topology with the geocoded features. Topology allows a GIS to do error correction. Topological functions allow the elimination of slivers and the use of fuzzy tolerances. Topology also allows adding raster-like attribute data to a vector data structures. An advantage is that overlap areas are cleaner and redistricting is easier.