This document discusses geo-referencing and geo-coding. Geo-referencing is the process of aligning raster images and vector data to real-world coordinates so they can be overlaid and analyzed with other geographic data in a GIS. There are two main types: geo-referencing raster images and geo-referencing vector data. Geo-coding involves assigning coordinates to point data, often by matching addresses. While geo-referencing aligns geographic images, geo-coding specifically matches addresses to latitude and longitude coordinates.
2. Contents
Geo-referencing
Need for Geo-referencing
Types of Geo-referencing
Methods
Steps for Geo-referencing
Geo-coding
Difference between the two
Geo-referencing for digitization
3. Geo-Referencing
Geo-referencing is the process of scaling, rotating, translating and
de-skewing the image to match a particular size and position
To Georeference means to associate something with locations
in physical space.
The term is commonly used in the geographic information
systems field to describe the process of associating a physical
map or raster image of a map with spatial locations
Georeferencing may be applied to any kind of object or
structure that can be related to a geographical location, such as
points of interest, roads, places, bridges, or buildings
4. Need for Geo-referencing
Geo-reference is used when establishing the relation between raster
or vector images by determining the spatial location of the
geographical features
This procedure is mandatory for data modeling in the field of
geographic information systems (GIS)
When data from different sources or time periods (like time series
satellite images) need to be combined and then used in a GIS
application, (e.g. for change detection, assess damages after a
natural disaster etc.), it becomes essential to have a common
referencing system
6. Geo-referencing Raster Images
A crucial element of any mapping project is registering a map with the correct
real world coordinates. This procedure is called geo-referencing. If the maps
are not geo-referenced, no other information can be displayed over or
positioned under the map coverage.
Depending on the source materials and the specifications of the project, maps
can be registered to either a coordinate system or to another base map such as
a digital ortho photo.
7. Geo-referencing Vector Data
Vector data can be geo-referenced (or rubber sheeted) to
real world coordinates. Vector data can be either rubber
sheeted to match existing base maps or the data may be
projected into a specific coordinate system.
8. Geo-Coding
Geocoding is the conversion of Geo-refencing (spatial information)
into digital form
Geocoding involves capturing the map, and sometimes also
capturing the attributes
Assigning spatial coordinates to point data
9.
10. Geocoding Methods for Maps
Digitizing
Scanning
Field Data Collection
Vector and Raster
In ArcView Feature Data Source, Image Data Source
Often involves address matching
11. Difference between the two
Geo-referencing: Matching geographic images to
coordinates
Geo-coding: Matching addresses to geographic coordinates
(latitude & longitude)
12. Geo-referencing for Digitization
What is digitization?
Capturing data by converting features on a paper map or (digital) aerial
photograph into digital vector format
Methods
Method Devices
Manual digitising • Coordinate entry via keyboard
• Digitising tablet with cursor
• Mouse cursor on the computer
monitor: on screen digitising (heads-up)
• Digital photogrammetry
Automatic digitising • Scanner
Semi-automatic
digitising
• Scanner and line-following software
13. The image is a photo of the 3D model
Georeferencing: What to do?
Data are not yet structured into classified
and coded objects
Image data has to be vectorised and structured first
14. Conclusion
Used to convert the entire map onto a real-world co-ordinate system
With Georeferencing you can align geographic data to a known coordinate
system so it can be viewed, queried, and analyzed with other geographic data
Geocoding is a GIS operation for converting street addresses into spatial data
that can be displayed as features on a map, usually by referencing address
information from a street segment data layer