ArcGIS Pro

What is Georeferencing?

Georeferencing is the process of assigning x, y coordinates to a raster file, such as an aerial photograph, scanned historical map, etc. so GIS software can place the resulting georeferenced file in its specified location on a map. The georeferencing process involves assigning control points to the raster image and matching them to control points on an existing georeferenced data set.

 

Georeferenced fire insurance map of Harvard Square (1885). Map from Insurance Maps of Boston, Vol. 4.
 

Learn More about Georeferencing

Add Raster Data in ArcGIS Pro (e.g., historical map, aerial photograph)

1. In ArcGIS Pro, go to the the Map menu > Add Data to add your raster file to your project.
2. Select Yes if you're prompted to calculate statistics for the raster.
3. A pop-up window will display indicating that the raster you added to your project has an unknown coordinate system. This is a standard message when georeferencing (see "unknown coordinate system" below) for more information.

Unknown Coordinate System Message

When you add an image into ArcGIS Pro, a pop-up window will appear stating that there's an unknown coordinate system. This is a standard message that appears when you add data into ArcGIS Pro that's missing spatial reference information. 

Since the software doesn't know "where" to place your map, it will be placed at the default location (0,0), the intersection of the Equator and the Prime Meridian. Georeferencing is one of the processes that can be used to help supply spatial reference information (e.g., coordinates, datum, projection, etc.) to your map file so it overlays in the correct location on the map. 

Prepare a Raster for Georeferencing

1. Click Georeference to open the Georeference toolbar.

1. Click Set SRS to confirm that you’ve set the spatial reference for your map. Note: Nothing will happen if you've previously set your SRS.
   
    
2. In the Georeference tab, click Fit to Display (in the Prepare group) to overlay the map on your current view of your study area.
   
    
3. You can use the Move, Scale, and Rotate tools to further adjust the display of your overlaid map.
    
4. Switch to the Map tab to use the navigate tools (zoom in / out, etc.) to adjust the view of your map.
   

Georeference a Raster

You can georeference a raster by visual reference, supplying coordinate data, etc.

Export a GeoTIFF

Once you've completed the georeferencing process, you can export your georeferenced raster as a GeoTIFF. A GeoTIFF is a geospatial image file format that has coordinate data embedded into the file. When you add a properly georeferenced raster (in GeoTIFF format) to a new map project, your raster will overlay in the correct location on the map.
 

1. Right-click on your map layer in the Contents pane.

2. Select Data > Export Raster to open the Export Raster pane.
   

3. In the Export Raster pane, make sure that the Output Raster Dataset is saving to your project folder (or the Home Folder if you're using Amazon AppStream). Confirm that the Coordinate System is set to the correct coordinate system (e.g., WGS_1984_UTM_Zone_20N).
   

4. Set the NoData value drop-down menu to 0. If you don’t populate this field, a black border will display around your map.
          
    

5. Choose TIFF as your output format. Change the Compression Type to LZW. This will decrease the file size of your exported file.
   

6. Click Export to export your raster. The export process will create a GeoTIFF of your map.
    

Learn More about Exporting GeoTIFFs

Crop Your Georeferenced Map

If you'd like to crop a border from your map, you can follow the steps for Perform a Raster Clip.