The technique of assigning geographic positional information to raster data based on a predetermined coordinate system is known as georeferencing.
This georeferencing process is typically performed with GIS software such as QGIS, ArcMap, or ArcGIS Pro and is a powerful way to add value to scanned images of paper maps, printed aerial photos, and other geospatial raster data that lacks coordinate information by preparing the data for GIS-based analysis and digitizing operations.
The georeferencing procedure may also be used with the clipping raster data process to eliminate undesirable areas of a scanned picture and the image compression process to minimize the raster file size.
The georeferencing procedure differs widely depending on the GIS program you’re using and the properties of the raster data you’re working with.
Although not all maps provide geographic coordinates for the map corners, and others do not provide any coordinate information at all, these sorts of maps may nevertheless be georeferenced using a slightly different method.
In general, three basic sorts of information that may be utilized to reference geographical objects can be recognized.
a) Geometrical data specifies the geometric qualities of an item, such as the layout and geometry of a road section.
b) Topological information is concerned with the properties of objects that are preserved despite continuous deformations; in the context of georeferencing, the graph structure induced by networks of certain geographical objects, such as roads or rivers, is of primary concern for topological investigations.
c) Semantic information refers to a variety of semantic features that may be linked to a geographic location, such as a place name or a road.
In order to uniquely identify a geographical item, common georeferencing methods consider at least one category, but frequently a mixture of these forms of information.
Matching is the process of detecting geographical items and allocating them to certain places. When creating a map from the ground up, the author identifies geographical items, places, and relationships between them.
Georeferencing is commonly done with a geodetic reference system like WGS-84 (National Imagery and Mapping Agency 2000), which consists of a standard Earth coordinate frame, a reference ellipsoid, and a geoid that establishes a nominal sea level.
Other reference systems could be used depending on the application sector. Navigation devices can be employed for data collecting in the map-making process to some extent.
GPS trackers provide WGS-84 geodetic reference system coordinates that may be linked to a specific geographic location on a map.
An assignment between geographical items and geographical places is the result of a matching procedure.
Types of Geo-referencing
A) Vector Georeferencing
B) Raster Georeferencing