The process for georeferencing raster data to a reference layer is documented in the book 'Using ArcMap'. However, it is also possible to georeference raster data to known points without a reference layer.
The coordinates to which the raster image will be georeferenced and the coordinate system (projection) of those coordinates must be known before beginning this process.
- Open ArcMap with a new, empty map, and add the raster data to be georeferenced to the ArcMap session.
- Open View > Data Frame Properties > Coordinate System tab > Predefined, and browse to the Coordinate System of the output coordinates you will use in this process.
For example, if the output coordinates are in NAD 1983 UTM Zone 15N, you will set the projection of the Data Frame to that coordinate system.
- Add the Georeferencing toolbar to ArcMap.
- Zoom in to the first point on the raster image that will be used as a control point, then click the Add Control Points tool.
- Place the cursor over the first control point in the raster and right-click.
- Move the curser slightly and right-click.
- Select Input X and Y.
- Enter the known output coordinates for this control point and click OK.
- Enter enough points for the desired transformation order.
For further information on the number of control points needed, refer to ArcGIS Desktop Help: About georeferencing > Transforming the raster.
- Click View Link Table to evaluate the transformation.
- Click the Georeferencing menu and select the Update Georeferencing option to save the transformation information with the raster.