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Georeferencing is the process of aligning spatial data (layers that are shape files: polygons, points, etc.) to an image file such as an historical map, satellite image, or aerial photograph. This document describes the basic steps for Georeferencing an image using ArcGIS.*
Add
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a Basemap and Image to the Map Project
- Click on View → Toolbars → Georeferencing
- Add a Georeferenced Basemap to your new Map Project. We recommend adding the ESRI Imagery World 2D Map or ESRI Street Map World 2D from the ESRI servers.
- Add the image you want to Georeference to your map project.
Raster images - such as .jpg, .tiff, or .png files (all of these are image file types), are actually made up of multiple layers. Click once on the name of the image file and then add it to your map project. If you double click on the image file when using the Add Data feature in ArcMap, you will see something like this:
Raster Image Band Layers
The 3 bands represent layers that make up the image file. You can see the name of the file in the Look In: field at the top of the dialog box. To successfully add the file as a single, unified whole, do the following:
- From this view, click on the Up One Level button
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- You will see the file name of the image again. Simply highlight
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- the file name by clicking on it once
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- .
- Click Add to add the file to your Map Project.
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- Open all spatial layers you will use to georeference the image.
- Zoom in to the approximate area that is covered by the image to which these layers will be added. This does not have to be exact as it is done just to provide you with an easier workspace.
- Adjust the color and shape of any points so that they will be visible when displayed on the image.
- Polygons will be easier to use if you make them "hollow" (hollow is a choice in the list of fill colors for symbols). Also choose a color and width for the line around the shape that can be seen against the image layer.
Control the Image Size and Position in the Map Project
The Scale Tool
Many times, images added to a Map Project appear so large in the Data Frame (the main viewing area) of ArcMap that they cover the entire viewing surface. You can re-size the image by using the Scale Tool in the Georeferencing Toolbar.
Scale Tool
Make an Image Smaller
- Select the Scale Tool from the Georeferencing Toolbar.
- Move the cursor to the corner of the image.
- Click and drag from the corner to the center of the image.
- Release the mouse. The image will resize.
Make an Image Larger
- Select the Scale Tool from the Georeferencing Toolbar.
- Move the cursor to the center of the image.
- Click and drag from the ccenter to beyond one of the outside edges. The further outside the edge of the image you drag, the larger the image will become.
- Release the mouse. The image will resize.
The Shift Tool
You can move an image file around the Data Frame using the Shift Tool to reposition it for the purposes of viewing Control Points on your image and Basemap simultaneously.
- Select the Shift Tool from the Georeferencing Toolbar.
- Click and hold the mouse on part of the image. Drag the cursor to the desired area in the Data Frame.
- When you release the mouse button, the portion of the image on which you clicked and dragged will move to the area where the cursor was when you released the mouse.
The Rotate Tool
To orient an image, use the Rotate Tool to turn the image to match the Basemap.
- Select the RotateTool from the Georeferencing Toolbar.
- Click and drag the image to rotate it in the Data Frame.
- When you release the mouse button, the image will rotate.
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Adding control pointsThis is the process of matching points on the image layer to corresponding points on the shape layers. From the Georeferencing toolbar select the
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