ArcMap GeoReferencing Tutorial for a Digitized Map Image

Files you will need for this tutorial: Delaware Co. 2012 TIGER Line data; Muncie, IN HOLC map

First off, you will have to get your own data, depending on your assignment choice. Here are the HOLC maps to choose from. For your road maps, go to the U.S. Census site and download the appropriate TIGER road shape file. Google something like “TIGER Line shapefiles.” When you get to this page, use the Web interface.

Here I chose All Roads, rather than the relatively limited Primary and Secondary. The screen will be a bit more cluttered, as you will see, but it will give you more opportunities to match georeference points. You might do just as well with Primary and Secondary.

Open up ArcMap and create a new Blank Map.

Here is your fresh, blank map file (.mxd). To the left is the Table of Contents, in the middle is the Data View, and to the right I have open ArcCatalog (that is optional right now).

You will want to add data, so click on the icon/button in the toolbar at the top of the screen under the Selection menu with the yellow diamond and the black plus sign. You may have to add a connection telling ArcMap where to find your data, in which case you would click the yellow folder with the black plus at the top of the dialog window. Navigate to the location of your Tiger Line shape file and add it to the map. Here, a shape file looks like a single file, but in Windows Explorer you will see that it comprises a bundle of 3 to 6 files, only one of which has the .shp file extension.

Here you see the road network for Delaware County. You can change the color of the roads by clicking on the little blue line in the Table of Contents. You can always return to this zoom extent by right-clicking the shape file in the Table of Contents and choosing Zoom to Layer.

Now we want to zoom into the city of Muncie (the county seat and city in the center of the county). Select the + magnifying glass in the toolbar on the upper left. You can either keep clicking to zoom in step-by-step or you can click and drag rectangular window in the Data View to choose the extent of the zoom.

Once we’re looking at Muncie, we can add the image of the archival map. Choose the Add Data button at the top again and navigate to the .jpg file. Don’t double click the .jpg because it will give you the choice of just adding the red, green, or blue channel of the image. Just add the .jpg using the Add button.

You’ll get this little window; select No, as it will not make any performance difference for us.

Now you’ll need to open the Georeferencing toolbar. In the Customize menu, choose Toolbars, then choose Georeferencing and the toolbar will appear at the top of your map window.

From the Georeferencing drop down menu on the toolbar, choose Fit to Display. If for some reason you have more than one image file in the Table of Contents, make sure the correct one is selected on the toolbar.

The image will appear behind the road shape file. You can click on the map layer in the table of contents to tick and untick the box and make the map image layer appear and disappear. This will allow you to find roads that match up between the two. You can zoom in to see in greater detail, but you must visually find corresponding roads on the map image and the road shape file.

To perform the actual georeferencing, you must click the button on the georeferencing toolbar with the two plus signs. This will allow you create control points connecting points on the map image and the shape file. Click first on the map image and second on the corresponding point on the shape file. You will need between 4 and 8 matching point pairs and you should start with point pairs on the far edges of the map. This will enable gross changes and warping of the map image as you tell ArcMap how the JPG should be stretched.

Here the shape file layer has been unticked so scrutinize the map for correspondences on the east side of the map and city.

After a few control points are established, the map has begun to warp and does not look great. However, it will improve and match up better with more control points. After about 4 control points at the edges, you can begin to fine-tune with interior, smaller adjustments in the interior.

If you make an error, you can click the button on the right end of the GeoReferencing toolbar that will list the control points and allow you to delete points created in error. You can see in the Data View that the maps are starting to line up well.

Here you can see that with a few additional control points, the map lines up quite well. It is almost impossible to make a perfect match, but it is key to find the point at which there is no more benefit or improvement with an additional point.

Be sure to save your map (.mxd) file, and you can save your georeferenced map by right-clicking the layer in the Table of Contents, choosing Data and Save or Export.