Geo referencing by Mashhood Arif

When you georeference your raster data, you define its location using map coordinates and assign the coordinate system of the map frame. Georeferencing raster data allows it to be viewed, queried, and analyzed with your other geographic data. The georeferencing tools on the Georeference tab allows you to georeference any raster dataset.

In general, there are four steps to georeference your data:

Add the raster dataset that you want to align with your projected data.
Use the Georeference tab to create control points, to connect your raster to known positions in the map
Review the control points and the errors
Save the georeferencing result, when you are satisfied with the alignment.

1. Geo-Referencing & Geo-Coding

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

5. Types of Geo-referencing Two types: Geo-referencing Raster Images Geo-referencing Vector Data 

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. Geocoding Methods for Maps Digitizing Scanning Field Data Collection Vector and Raster In ArcView Feature Data Source, Image Data Source Often involves address matching

10. Difference between the two Geo-referencing: Matching geographic images to coordinates Geo-coding: Matching addresses to geographic coordinates (latitude & longitude)

11. 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) Digita l photogrammetry Automatic digitising Scanner Semi-automatic digitising Scanner and line-following software

12. 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 structur ed first

13. 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