The document outlines the process of georeferencing, which involves aligning raster datasets to real-world coordinates for accurate geographic positioning. It describes the general steps for georeferencing, including adding control points and saving alignment information, as well as two types of georeferencing: absolute and relative. Ground control points (GCPs) are defined as known locations used to geo-reference image data sources.

2. WELCOME

3. GEOREFERENCING
GIS
(BASIC COURSE)
By
Dr. Jaweria Shamshad
Ph.D. Environmental Sciences
College of Earth and Environmental Sciences
University of the Punjab, Lahore
3

4. Dr. Jaweria Shamshad, CEES , University of the Punjab
Georeferencing
"Georeferencing is the process of aligning the raster dataset, with the help
of real world coordinates, to its actual position on the earth (globe).”
 Raster data is commonly obtained by scanning maps or collecting
aerial photographs and satellite images, these datasets don’t normally
contain spatial reference information.
 With aerial photography and satellite imagery, sometimes the location
information delivered with them is inadequate and the data does not
align properly with other data you have.
 When you geo-reference your raster dataset, you define its location
using map coordinates and assign the coordinate system of the data
frame.
 Georeferencing raster data allows it to be viewed, queried, and
analyzed with other geographic data.

5. Dr. Jaweria Shamshad, CEES , University of the Punjab
Steps to do georeferencing
The general steps for georeferencing a raster dataset are:
 Add the raster dataset that you want to align with your projected
data in ArcMap.
 Add control points that link known raster dataset positions to
known positions in map coordinates.
 Save the georeferencing information when you’re satisfied with
the alignment (also referred to as registration).
 Optionally, permanently transform the raster dataset.

6. Dr. Jaweria Shamshad, CEES , University of the Punjab
Types of georeferencing
There are two general types of georeferencing, that are:
1) Absolute Geo-referencing
 The image is georeferenced by taking GCPs (Ground Control
Points) with the help of GPS device, Google earth, Topo sheets
etc.
2) Relative Geo-referencing (Image to Image Registration)
 The image is georeferenced with the help of another already
georeferenced image

7. Dr. Jaweria Shamshad, CEES , University of the Punjab
GCP (Ground Control Point)
 Ground Control Point (GCP) could be defined as a point on the
surface of the earth of known location (i.e. fixed within an
established co-ordinate system) which is used to geo-reference
image data sources, such as remotely sensed images or
scanned maps.
It is also known as Control Point (CP).

8. Dr. Jaweria Shamshad, CEES , University of the Punjab
GCP (Ground Control Point)
 Ground Control Point (GCP) could be defined as a point on the
surface of the earth of known location (i.e. fixed within an
established co-ordinate system) which is used to geo-reference
image data sources, such as remotely sensed images or
scanned maps.
It is also known as Control Point (CP).