What is Georeferencing?
By James Spokes, CEO, Monarcha
Georeferencing is the process of aligning a scanned or digital image (typically a map, aerial photograph, or satellite image) to a real-world coordinate system. The result is a file that knows where it belongs on the Earth's surface, enabling it to be overlaid with other spatial data in a GIS (Geographic Information System).
Why does georeferencing matter?
Millions of maps exist only as scanned images or paper documents. Geological surveys, mine plans, zoning maps, historical plats, and topographic sheets, many created decades before digital mapping existed, contain invaluable spatial information. But without georeferencing, that information is locked inside a flat image with no spatial context.
Once georeferenced, these maps can be layered with modern satellite imagery, drilling data, parcel boundaries, and other GIS datasets. This unlocks analysis, measurement, and decision-making that simply isn't possible with a paper map or an unregistered scan.
How does traditional georeferencing work?
The conventional approach involves a GIS technician manually identifying Ground Control Points (GCPs), locations that are visible on both the source image and a reference dataset with known coordinates. Typically, this means finding grid intersections, survey markers, road intersections, or other identifiable features and matching each one to its real-world coordinates.
The technician then applies a mathematical transformation (polynomial, affine, thin-plate spline, or rubber-sheeting) to warp the image so that the GCPs align with their real-world positions. The quality of the result depends heavily on the number and distribution of GCPs, the skill of the technician, and the characteristics of the source map.
What makes it difficult?
Legacy maps come in an enormous variety of projections, datums, and coordinate systems. A 1960s geological survey map from Chile might use a local datum. A county plat book from Georgia might be in state plane coordinates. A mine plan might use a completely custom local grid with no standard EPSG code.
Identifying the correct coordinate reference system (CRS) and finding enough well-distributed control points is time-consuming and error-prone. A single archive of several hundred maps can take a GIS team weeks or months to process manually.
How AI is changing georeferencing
Modern computer vision and AI techniques are transforming this process. At Monarcha, we've built AI models that can read marginal notations, detect grid ticks, parse coordinate labels, identify projection metadata, and automatically compute ground control points, all without manual intervention.
The result is georeferencing that takes seconds instead of hours, with accuracy that matches or exceeds manual GCP placement on most map types. This makes it practical to process entire map archives at scale, something that was previously cost-prohibitive for most organizations.
What comes after georeferencing?
Georeferencing is often just the first step. Once a map is spatially registered, the next step is digitization: extracting the features on the map (geological units, parcel boundaries, road networks, drill hole locations) into vector layers that can be queried, analyzed, and integrated with other datasets.
Together, georeferencing and digitization turn a static image into living spatial data, ready for GIS analysis, resource modeling, permit review, or any other spatial workflow.