Geocoding involves converting spatial information, such as drawings, maps, photographs and addresses, into digital form for use in geographical information systems (GIS) using scanning, digitizing and address matching operations.
Scanning
Scanning is the process by which raster data is captured from a paper map. Raster data is a way of representing the earth's surface by subdividing into small pixels (or a grid).
Once a paper map has been scanned it can be added into a GIS. At this point the image needs to georeferenced (the user tells the GIS where to locate the image). This is done by inputting the known coordinates of control points on the image.
Digitising
Digitising is where points or line features are traced either directly from paper maps or from scanned images of the maps to create vector data. Vector data divides space into discrete features, usually points, lines or polygons.
Address matching or geo-coding
Address matching or geocoding uses the recorded address in conjunction with a digital map or computerised list of addresses to place a street address onto the map in a known location.
This usually involves the matching of two files. One file contains the addresses of interest and the other file contains a list of addresses and their coordinates. This process often uses commercial software such as QuickAddress.
There are a number of address datasets, including:
If only the postcode is known for a particular set of data then this can be mapped to the centroid (centre) of the unit postcode. Existing data to enable this includes:
The level of success often depends on the quality of the original address data. See our collecting geospatial data for information.