GIS is a computer system that captures, stores, manages, analysises and displays all kinds of spatial or geographical data and all the data is aggregated into a location reference system (longitude and latitude). 
 
GIS aids in:


Maximising the efficiency of planning and decision making
Providing efficient means for data distribution and handling 
Elimination of redundant data bases in order to minimise duplication
Integrate information from many sources 

Concepts of Geodesy
 
There are two types of datum:
- Horizontal datum measures a point on earths surface in longitude or latitude. 
- Vertical datum measure elevations or depths on the surface.
 
Distortion Types on Maps:


Conformality - Accuracy of the shapes of the map
Distance - Accuracy of measured distances on the map to actual distance on ear
Area - The area represented is proportional to the area on the earth
Directions - The directions between points is accurate represented on the map

Types of Geometric Transformation

Equal Area - allows rotation of a rectangle and keeps it size and shape
Similarity Transformation - allows rotation of a rectangle and keeps its shape, but not size
Affine Transformation - allows angular distortion of a rectangle, but keeps its parallelism of lines
Projective Transformation - allows angular and length distortions, allowing the rectangle to be transformed into an irregular quadrilateral 

Affine Transformation is most common and control points have a key role in determining the accuracy of an affine transformation.