Georeference is another name for spatial reference or geographic reference and describes the position in a reference system . A spatial reference turns data and information into basic geospatial data and specialist geospatial data . This means that they relate to a position in geographical space and are geo-referenced .
The spatial reference can be direct or indirect.
- A direct spatial reference is used when data are assigned to coordinates.
- The spatial reference is indirect if the information does not relate to permanently fixed coordinates.
Direct spatial reference
A direct spatial reference is created when the spatial position of the information on earth is realized ( georeferenced ) using two or three-dimensional coordinates . An example of a direct spatial reference is the unique location of an address based on its geographic coordinates or the arithmetic assignment of pixels of a digital image (e.g. scanned maps or aerial photographs ) to real (world) coordinates using control points or world files . This assignment enables a GIS to superimpose / locate different pixel images, also of different scales and origins, precisely and true to scale, for evaluation and further processing in a uniform coordinate system .
Indirect spatial reference
An indirect spatial reference arises when the information relates to not precisely defined coordinates such as B. refers to an administrative area (country, city), to a road kilometer marking or to a house number range, a block page or an area from the aggregation of block pages (e.g. postcode area) in the so-called small-scale breakdown of the municipal statistics. The indirect spatial reference is mainly used in official statistics and spatial observation for the assignment, aggregation , analysis and visualization of specialist geospatial data and is the basis of statistical information systems .
Communal spatial reference
The communal spatial reference system uses addresses (with coordinates: geographic reference data with direct spatial reference) and a hierarchical structure of the urban area from the residential / building block to the district (thus geographic reference data with indirect spatial reference) for the spatial allocation of small-scale data.
Thus the individual data from administrative registers as can be without capturing coordinate geodata of the municipal statistics assign spatially, aggregate and analyze about the addresses, the individual data can also be geo-referenced to.
In the official statistics, the data for administrative areas (usually on the NUTS levels, municipal on city districts, electoral districts, etc.) are aggregated. For the register-based census 2011 ( population census ), an "address and building register" is being set up as a reference system for merging the register data.