Geo-Referencing & Geo-Coding

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

Geo-ReferencingGeo-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 locationsin physical space.

The term is commonly used in the geographic informationsystems field to describe the process of associating a physicalmap or raster image of a map with spatial locations

Georeferencing may be applied to any kind of object orstructure that can be related to a geographical location, such aspoints of interest, roads, places, bridges, or buildings

Need for Geo-referencingGeo-reference is used when establishing the relation between raster

or vector images by determining the spatial location of thegeographical features

This procedure is mandatory for data modeling in the field ofgeographic information systems (GIS)

When data from different sources or time periods (like time seriessatellite images) need to be combined and then used in a GISapplication, (e.g. for change detection, assess damages after anatural disaster etc.), it becomes essential to have a commonreferencing system

Types of Geo-referencingTwo types:

1.Geo-referencing Raster Images

2.Geo-referencing Vector Data

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 mapsare not geo-referenced, no other information can be displayed over orpositioned under the map coverage.

Depending on the source materials and the specifications of the project, mapscan be registered to either a coordinate system or to another base map such asa digital ortho photo.

Geo-referencing Vector Data

Vector data can be geo-referenced (or rubber sheeted) toreal world coordinates. Vector data can be either rubbersheeted to match existing base maps or the data may beprojected into a specific coordinate system.

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

Geocoding Methods for Maps Digitizing

Scanning

Field Data Collection

Vector and Raster In ArcView Feature Data Source, Image Data Source

Often involves address matching

Difference between the twoGeo-referencing: Matching geographic images tocoordinates

Geo-coding: Matching addresses to geographic coordinates(latitude & longitude)

Geo-referencing for DigitizationWhat is digitization?Capturing data by converting features on a paper map or (digital) aerialphotograph 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

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

ConclusionUsed to convert the entire map onto a real-world co-ordinate system

With Georeferencing you can align geographic data to a known coordinatesystem so it can be viewed, queried, and analyzed with other geographic data

Geocoding is a GIS operation for converting street addresses into spatial datathat can be displayed as features on a map, usually by referencing addressinformation from a street segment data layer