Grids must often include redundant or missing data. Grid compression techniques used in GIS are run-length encoding and quad trees. Lines and areas are built from sequences of points in order. Lines have a direction to the ordering of the points. Polygons can be built from points or lines.
Vectors can store information about topology.
At first, GISs used vector data and cartographic spaghetti structures. Points, lines, and areas can each be stored in their own files, with links between them. Arc junctions are only at nodes. Vectors just seemed more correcter. TIN must be used to represent volumes.