What are some best practices for georeferencing images in ArcGIS?

1 Choose a suitable image

The first step in georeferencing is to choose an image that is relevant, clear, and has enough details to match with your base map. You can use any raster format that ArcGIS supports, such as TIFF, JPEG, or PNG. However, some formats may have limitations, such as compression, color depth, or resolution. You should also consider the size and scale of the image, and how it fits with your map extent and projection.

3 Apply a transformation

After adding enough control points, you need to apply a transformation, which is a mathematical operation that adjusts the image to fit the base map. You can use the Georeferencing toolbar to select a transformation type, such as affine, projective, or polynomial. The transformation type depends on the shape and distortion of the image, and the number and accuracy of control points. You can use the Link Table or the Residuals Table to check the quality and error of the transformation.

4 Adjust the image

Sometimes, you may need to adjust the image further, especially if it has irregular shapes, such as curves, bends, or angles. You can use the Spatial Adjustment tools to edit the image geometry, such as moving, scaling, rotating, or warping. You can also use the rubbersheeting or edge-matching methods to align the image with adjacent features or boundaries. You should use the Spatial Adjustment tools carefully, as they can affect the accuracy and resolution of the image.

5 Save the georeferencing

The final step is to save the georeferencing, which is the process of storing the spatial information of the image in a file. You can use the Georeferencing toolbar to save the georeferencing in different ways, such as updating the georeferencing, rectifying the image, or creating a world file. The saving method depends on your needs and preferences, such as preserving the original image, creating a new image, or adding a spatial reference file.