What is Georeferencing in GIS? Advantages and Disadvantages of Georeferencing
What is Georeferencing in GIS? Advantages and Disadvantages of Georeferencing
What is Georeferencing in GIS?
Georeferencing is the process of adding coordinate information to a digital image so that it can be accurately displayed on a map.
This is typically done by attaching known latitude and longitude points to the image, but can also be done with other coordinate systems such as UTM or State Plane.
Once the image has been georeferenced, it can be used in a GIS to spatially analyze or map features in the image.
A software can gradually warp the image to fit other spatial datasets by associating features on the scanned image with real-world x and y coordinates.
It is therefore is the process through which geographical information systems use the positions of some reference points to fix the geographic location of each topographic feature.
The georeferenced maps are used for applications such as planning, land use management, environmental analysis, and disaster risk management on a global scale.
Steps of Georeferencing in GIS
There are six steps in georeferencing; they are
- Selection of appropriate imagery
- Acquisition, rectification and enhancement of imagery
- Georeferencing analysis
- The statistical analysis and modeling of the data
- Adjustment and reprojection of the georeferenced data
- Publication of the results in an output map format using the most appropriate software for the intended end-user (MapInfo, ArcGIS, Google Earth).
Georeferencing Software in GIS
- Banner is the most used georeferencing software in GIS. It is very effective and has the real time capability.
This software can easily answer the real time queries and spatial data acquisition from the aerial imagery. In this, it captures all important details of images such as latitude, longitude, altitude and pixel size.
The major drawback of Banner is that it doesn’t work in Internet Explorer version 8 or below due to its HTML5 dependency. Hence, it can be downloaded only on Microsoft Windows operating system.
- GIS can be easily georeferenced using Bing Maps. It has a very efficient functionality and also allows beyond the standard networks access of imagery online.
This software is most familiar with geospatial data and digital maps. It can work with many types of data by associating them with real-world coordinates.
- The NIMA tool is the still the most commonly used GIS Georeferencing software. It is a very efficient and time saving tool.
It has many functions, some of them are rectification, warping, reprojection and geocoding among others.
The drawback is that it cannot be used on Mac Operating system as it has a Windows-only functionality.
- The other georeferencing software available is MultiMap, TerraMap and Mapwarper. They are very efficient and allow making a digital map from an aerial or satellite imagery.
This software can work with any imagery available on any media format like .jpg, .tif, or .bmp.
- The GIS software uView has many advanced functions and is also easy to use. It is used for georeferencing photos shot with a digital camera. It is a very effective tool available for GIS georeferencing.
- The GMap has an efficient functionality and is able to perform different tasks related to the orientation of a picture or digital map.
- The ESRI ArcGIS software also has many functions. Some of them are image rectification, image mapping and image geo-referencing among others.
This software is very efficient, and can be used on different platforms such as Windows, Linux, Mac and many others.
- The QGIS is easy to use and has many functions with simple user interface. It has a many advanced tools that are not available in other georeferencing software. Some of these tools include virtual globe, vector editing and attribute management among others. It can be used on various operating systems including Microsoft Windows, Mac OS X, Linux and Unix among others.
- The Geotoolkit.org software is used for georeferencing of the aerial images and satellite images (as vector data). It is a very efficient software with its own database of images and maps among others.
- The GNIS (Geographic Names Information System) is also an important tool for georeferencing maps and satellite images as vector data.
- The GIS software ArcMap is a very efficient tool with many advanced functions. It is used for georeferencing of different images and maps among others.
- The geospatial software Tesseract is used for georeferencing maps and satellite images as vector data among others. Tesseract is capable of georeferencing aerial, satellite, and high-resolution mapping (LANDSAT, SPOT) imagery among others.
- ArcGIS Server is powerful geospatial server software that has many functions and features. It is used for georeferencing of all types of image data.
- Google Earth is a very efficient software for georeferencing images and maps among others.
Types of Georeferencing in GIS
There are two types of georeferencing in GIS namely vector and raster referencing
Vector Referencing
Vector referencing is the process in which a digital map is georeferenced using the features from another map or image.
It is done by comparing the features from various sources such as scanned maps, satellite images and aerial photos among others.
Then, by identifying common objects in different images, it will be possible to associate real-world x and y coordinates with those objects that are common to multiple images. This step will then result in the coordinates conversion of one feature to a location on earth that can be compared with other geographic resources. Vector referencing is used for many data that include geographical features like roads, physical features like oceans and rivers among others.
Raster Referencing
Raster referencing is the process in which a digital map is georeferenced using a grid of cells or pixels from another source.
This type of georeferencing can be done on images with large areas such as satellite images or aerial photos and maps among others.
There are two types of raster reference; they are
- Grid (cell-based) reference
In this type of georeferencing, images are divided into a grid of cells. Each cell has its own coordinates in x and y. Thus, it would be possible to associate the coordinates with a grid cell from the map used for referencing.
- Shift-register (snapshot) reference
In this type of georeferencing, an image is taken in a certain position and orientation point which is the origin of the compass direction. These coordinates are then associated with the grid cell from a map.
Applications of Georeferencing
- Georeferencing allows the integration of spatial data from different sources. It allows for the use of data for a variety of purposes such as analysis, planning, decision making and documenting among others.
- Georeferencing also makes it possible to have standardization in the spatial data by allowing it to be compatible to any software used in GIS without causing difficulties.
- Georeferencing facilitates easy sharing of spatial data among people who can then use it for different purposes including decision making and documenting among others.
- Georeferencing allows for easy location of a particular house or business by providing its coordinates and description among others.
- Georeferencing also allows to coordinate between different data sets on the same map.
- Georeferencing also allows for using the spatial data to easily identify areas of interest in a map or image among others.
- Georeferencing helps in developing new forms of spatial data that can be used for analysis, planning and documentation among others.
- Georeferencing also facilitates easy management of spatial data among other users such as geologists, archeologists, planners and engineers among others.
- Georeferencing also enables the geographic information system to easily incorporate data from different sources including satellite images and maps into a single database.
Methods of Georeferencing in GIA
There are a number of methods to georeference maps in GIS. GIS programs and products support the creation of identifying GPS (geographic position system) coordinates for each point on the map corresponding to a particular database from which the data was created.
Manually
By using this method, the user has to place ticks on the map where he wants each feature or object to be located according to his own database. For example, the user can manually place ticks on the map to create a new point so that its X and Y position corresponds to existing points in the existing database.
Automatically
Georeferencing GIS can also be used here. It is used for georeferencing maps by using GPS, among others.
Interpolation
Georeferencing GIS is also possible using this method. It is used for georeferencing by using interpolation.
It is the process of assigning coordinates for a location near an existing point on the map so that it falls within a specified tolerance of that point.
Grid reference
In this method, the coordinates of a particular point on the map is interpolated by using several other existing data points in the same way that grid geometry is used to construct a plot of an area on a map.
Advantages of Georeferencing in GIS
Georeferencing has many advantages in GIS.
- Confidentiality
Georeferencing makes it possible for GIS to provide accurate coordinates in a secure manner.
- Security
Georeferencing GIS makes it possible for GIS to provide reliable coordinates using various sources such as maps, images, databases among others.
- Efficiency
Georeferencing lower processing costs because it does not require any additional work in creating the data sets for new point locations, corresponding to existing points that are already in the database.
- Accuracy
It is used for accuracy of data sets due to the use of reference sources like maps and images among others.
- Simplicity
Georeferencing GIS can also be applied here. It is used for simplicity in understanding and processing geographical features such as roads, physical features among others on maps among other advantages in GIS.
- Real time data
Georeferencing has these particular advantages in GIS. It is used for real time data on maps, images among others.
- Availability of spatial data to users
Georeferencing in GIS can also be applied here. It is used for availability of spatial data to the user, who can retrieve the information about the spatial features on his own preference.
- Data integrity
Georeferencing GIS can also be used here. It is used for data integrity, which makes it possible to check the validity of spatial data in a secure manner.
- Simplified maintenance
It is used for simplified maintenance of spatial data and make it more visible for analysis among other advantages.
- Cost
It is used for cost saving because it reduces costs of third-party data providers, who have to purchase the data from other sources, using their own labor and costs.
- Compatibility of other datasets
It is used for compatibility of the spatial data, which makes it possible to share and compare the information on a map among other advantages in GIS.
Disadvantages of Georeferencing in GIS
Georeferencing has many disadvantages in GIS.
- High Processing Costs
Georeferencing GIS has this particular disadvantage in GIS. It is used for cost of labor, which is required in determining the position of each point on the map.
- Third-party data providers pay for the cost
Georeferencing also has disadvantage in GIS. It is used for third-party data providers who have to pay the costs of creating and updating data on the map, which is not their own work.
- Accuracy problems
It is used for the accuracy of spatial data because it does not meet the standards and produces erroneous or misleading results due to errors that are present.
- Privacy issues
It is used for breach of data privacy, which is an infringement on the right of an individual to control their personal information.
- Issues with reference
It is used for errors in the reference source which makes it hard to use and understand spatial data.
- Incompatibility of spatial data
Georeferencing GIS also has this disadvantage in GIS. It is used for incompatibility of the spatial data, which makes it difficult to share and compare the information because it is not compatible with other datasets, which leads to a problem in using it to obtain spatial data results.
How to Georeference an image in QGIS
In order to georeference an image in QGIS, you should follow these steps:
- Open QGIS and choose the main menu item Raster->Georeferencer.
- In the open dialog box, choose a raster layer to be used as a reference layer. If your reference layer is not already loaded into QGIS, you can load it through the Layer List.
- Choose a georeference algorithm and parameters in the Georeferencer dialog box, depending on the characteristics of your image.
- Preview the result in the Preview window.
- In the Georeferencer dialog box, click Next to see results or click Finish to completely georeference your image.
FAQs
What is Georeferencing?
Georeferencing is the process of assigning geographic coordinates to a feature in a spatial database. This can be done manually by referencing a known landmark or using GPS coordinates, or it can be done automatically using a technique called feature matching.
Once a feature has been georeferenced, it can be used in spatial analysis and mapping applications.
This is often done by matching features in the map to corresponding features in a separate, known coordinate system.
This process can be used to improve the accuracy of digital maps or to make existing maps compatible with new data.
It may also mean using a map and referencing it via GPS or other sources of positional information (e.g., mean lake level in a lake), and then recording the values of these coordinates into a database.
What are the different methods used for Georeferencing?
There are two main methods for georeferencing, which are numerical and non-numerical georeferencing. Numerical georeferencing is an estimate of the coordinates of a spatial feature using the map, images, and other new sources.
Non-numerical georeferencing is the process of finding the coordinates for spatial features (e.g. roads, buildings) that are already in a database.
Why is georeferencing important in GIS?
It is important in selecting spatial features on a map based on coordinates, not just the area where they are located.
What is the difference between geocoding and georeferencing?
Geocoding is the process of converting the description of a location (keyed or free text) into a set of geographical coordinates, while georeferencing is the process of finding the geographical coordinates of a spatial feature on a map.
Georeferencing is used in GIS because it makes it possible to understand and process geographical features such as roads, physical features among others on maps, and then use this information for different purposes.
What are the basic components of georeferencing?
Georeferencing GIS has basic components like geodetic datum, map projection, spatial reference systems among others.
What is the difference between Geodetic Datum and spatial reference system?
Geodetic datum is used for the establishment of a point on earth. A spatial reference system is used for describing a set of points and their relationships to each other in a geographic coordinate system.
Spatial reference systems are based on geodetic datums.
What is the difference between coordinate and scale?
Coordinate is a number that defines an object’s position on the surface of the earth. Scale is used for measuring the dimension or size of something. A scale is both a number and a measurement unit, while a coordinate can only be a number.
How is georeferencing used with GIS?
Georeferencing is used in GIS to get the geographical coordinates of features or points on a map. This information is used for different purposes.
Selecting and grouping spatial features based on this information is one of them, while you can use it to calculate the location of other features or even analyze the geographic distribution of locations.
How is georeferencing used for accuracy?
Georeferencing makes it possible to obtain more accurate results, which are based on more accurate geographical coordinates.
It is crucial for GIS applications that require the highest level of accuracy for their particular purposes, like hydrology and environmental analysis.
How is georeferencing used for privacy?
Georeferencing is used for data privacy because it protects the personal information of each individual.
For example, if you are extracting data about a town, you can note the coordinates for every house in that town instead of listing the address.
This information can only be disclosed to third-party vendors under specific circumstances and it is not necessary to collect it from every individual directly.
How do you georeference and digitize in Arcgis?
In order to georeference an image in Arcgis, you can do the following steps:
- Choose Add Imagery and then choose the image (e.g., aerial photograph) that you want to georeference in ArcMap.
- Choose the main menu item Data Management->Georeference->Fit Image
- Click Georeferencing and then click OK to preview your data.
- Click Next to see results or click Finish to complete the georeferencing process.
How do you use data frames in Arcgis?
In order to georeference an image in Arcgis, you should use data frames, which include reference layers and coordinate systems.
- Open GIS and choose the menu item Analysis->Geospatial Data->Data Frames -> New.
- Choose a data frame region and then choose the main menu item Data Management->Georeference->Fit Image.
- Click Georeferencing and then click OK to preview your data.
- Click Next to see results or click Finish to complete the georeferencing process.
