Raster and Vector Data Encoding Methods in GIS

Raster Encodings: Exhaustive Enumeration

This structure records each individual value for every cell in a raster dataset.

Raster Encodings: Run-Length

This procedure collects the thematic value for each row and the columns in which it repeats:

• If multiple values exist in a row, the first value is indicated, followed by its start and end columns.
• Subsequent values and their respective column ranges are recorded sequentially until the end of the line.

Raster Encodings: Quad-tree

This structure encodes data by identifying terminal nodes or homogeneous quadrants and assigning four specific parameters:

• Coordinates: The X and Y coordinates of one vertex (e.g., the lower-left corner).
• Level: A number defining the subdivision level of the space.
• Value: The thematic value assigned to the quadrant.

Vector Coding: Coordinate List

This method stores pairs of coordinates defining segments of geographical lines. To register an object, you must record its name, the number of vertices, and the coordinates for each vertex. For polygons, the first vertex coordinates must be repeated to indicate the cycle closure.

Vector Coding: Vertex Dictionary

This method records the coordinates of each vertex present in the source map only once. Each vertex is identified by a unique name or digit. Once established, a dictionary is generated, listing the vertices that comprise each spatial object.

Vector Coding: DIME

The Dual Independent Map Encoding (DIME) was the first system to link vector representation with topology. Its primary utility is representing polygons by creating a list of names and X, Y coordinates for each vertex.

Vector Coding: Arc-Node

In this system, the base element is a chain or arc of segments assigned specific topology. The second basic element is the node, which corresponds to vertices in previous encodings. Polygons are defined by the arcs that connect exit and destination nodes, further identifying the polygons located to the left or right of each arc.