Lecture 1

Lecture 3-4.

Vector and Raster Types of GIS
Data Structure and Applications

"Yes raster is faster, but raster is vaster, and vector just seems more correcter."

C. Dana Tomlin

Raster Data Model (GRID)

Main elements:

rows, columns;
geographic extent;
cell size;
cell value;

Advantages:

fast;
simple;
mathematic modeling is easy;
location-specific manipulation is easy;
fast data acquisition (i.e. via satellites, scanners, etc.);

Disadvantages:

large data sets;
changes in the data size leads to the change in data resolution;
coordinate transformation is difficult and time consuming;
raster data are not elegant for the map production;
combination of the raster data modeling results and relevant vector data can disagree spatially;

Vector Data Model. Arc/Node Data Structure.

Main elements:

Topologic Elements: points, lines, polygons;
Structural Elements: nodes, arcs;

Advantage:

more accurate;
little repetition;
efficient in data storage;
very suitable for plotting devices;
topolygy described explicitly;
excellent for map production;
coordinate transformation and rubber sheeting is easy;

Disadvantage:

complex data structure;
do not forgive topological errors;
display and plotting can be time consuming;
not good at representing continuous fields and surfaces;
spatial analysis and mathematical modeling is difficult;

Tables associated with Vector Data Model:

Polygon Topology (Attribute) Table;
Node Topology (Attribute) Table;
Arc Topology (Attribute) Table;

The Triangulated Irregular Network (TIN)

TIN structure is a vector-based topological data model that is used to represent terrain data.

TIN represents the terrain surface as a set of interconnected triangular facets.

TIN structure is a vector-based alternative to the traditional raster representation of terrain surface - Digital Elevation Model (DEM).

TIN is a result of interpolation between measured elevation values. Unlike DEM, composed of regular grid, TIN facets have different sizes depending on data density. Therefore, TIN can describe terrain surface better. At the same time TINs are much more complex than DEMs and their production can be time consuming.