GIS Tips & Tricks

A weblog dedictated to the lifelong pursuit of cartographic bliss in GIS.

Monday, October 24, 2005

Georeferencing an image in ArcMAP

Scenario: Someone gives you a hardcopy map with a couple of polygons hand drawn on it. They want it in the GIS so you can make a pretty map for them and run some analysis. What do you?

In my opinion, you bascially have three options:
1. Use a digitizing tablet;
2. Eye-ball it off the map – often called ‘heads-up digitizing’ or ‘on-screen digitizing’; or
3. Scan the map, georeference the image and trace the polygons.

I’m going to quickly run throught the third option. For fun let’s call this geotracing. If you don’t have a digitizer it’s probably the best option…besides I’ve never been a fan of the on-screen digimonkey thing.

So as I mentioned above you’ll need to scan the map. Hopefully there aren’t too many maps and the polygons are concentrated in smaller areas that fit nicely on your scanner. I would recommend scanning to JPEG or TIF either will do fine.

Okay now that you have your images saved let’s fire up ArcMAP and launch the GEOREFERENCING toobar. Right click on the main toolbar and select Georeferencing.

Add some topographic layers to your ArcMAP document. Depending on your map, normally roads, water features and contours will work well.

Add the image you want to georeference. Don’t worry about ArcMAP complaining about the image missing a spatial reference information.

Using the Zoom tools roughly navigate to the area where the polygon should be added.
On the Georeferencing toolbar select> Fit to Display


As a personal preference, I also like to have Auto Adjust selected.

Your image should now be visible behind your layer features.

Select the Add Control Points button.



Begin adding control points linking features on your image to the GIS layers. As you add more control points the image will begin to morph and shift to the correct location.

If you added an unlucky control point that you wish to remove you can deleted in the Link Table. Beside the Add Control Points button select the View Link Table button. Select the link you wish to remove and hit the delete button.



Once your are satisifed with how your image lines up to your spatial data, you may wish to save the rectified image. Georeferencing> Rectify… > Save. The rectified image will be saved as a TIF.

Now that the source image is rectified it’s simply a matter of tracing or ‘geotracing’ the polygon(s) of interest. To do this I create an empty polygon shapefile. ArcCatalog> Right Click> New> Shapefile> Name it and select feature type> Polygon. If you know the spatial reference information it would be a good idea to EDIT that information here as well.

Now that you’ve created an empty polygon shapefile, add it to ArcMAP, Start Editing on the EDITOR toolbar and ‘Create a new feature’ by geotracing the polygon on your georeferenced/rectified image. Save Edits, stop editing, et Voila! You probably want to add fields and attribute information to the new polygon(s) but you already know how to do that…don’t you?

32 Comments:

  • At 10:01 AM, Anonymous Anonymous said…

    Thanks, that's useful.

     
  • At 7:14 PM, Anonymous Anonymous said…

    This was a big help, thanks!

     
  • At 4:47 AM, Anonymous Anonymous said…

    Very useful indeed. George

     
  • At 10:08 AM, Anonymous Anonymous said…

    it was very useful, thanks from mexico Omar.

     
  • At 10:50 PM, Anonymous Anonymous said…

    Thanks - a fine tutorial (for getting a picture of sealevel pressure contours over the pacific - sure beats messing with gridded data in netCDF format)....

     
  • At 10:38 PM, Blogger samuraijosh said…

    thats useful but i have a problem cos everytime I rectify an image I get a black mask around the new image actually showing the location of the raw image. Any way round this?

     
  • At 2:50 AM, Anonymous Anonymous said…

    I wish ESRI help was this straightforward and helpful. Thanks.

     
  • At 2:04 AM, Anonymous georeferencing said…

    I am really happy to read a post on georeferencing an image in ArcMAP

     
  • At 1:05 PM, Anonymous Anonymous said…

    This is great, but does anyone know what the GeoMedia equivalent to this is? Or if there even is GeoReferencing for GeoMedia?

     
  • At 7:34 AM, Anonymous Anonymous said…

    Thanks a lot.It very greatly helped.

     
  • At 8:27 PM, Anonymous Anonymous said…

    Yes, the exact process is available in GeoMedia. Need a read/write connection to an Access database, load any scanned image (jpg, tif) etc. Use "Insert Interactive Image" under Tools, place roughly to scale where you want it. Then select Tools, Image Registration, give it a name, click "Add Points", need a minimum of 4 points between the image and the corresponding place on the "earth", double click to end, it calculates the amount of warping similar to the one screen shot then hit the Register button when happy with the results. Then if you want to convert it to a geotif, select the output to Geotiff option under Warehouse menu, name the image and hit save. Much easier if you add these 3 buttons to the toolbar using the customize command instead of hunting through the menus.

     
  • At 10:11 PM, Anonymous Image georectification said…

    Tools in ArcMap can easily reposition a CAD file and integrate it into that higher level without altering the CAD file. ArcMap snapping helps accurate placement of the CAD file which makes precise selection of control points based on existing geometry. The information provided was useful. Thanks for sharing.

    georeferenced data processing services

     
  • At 7:41 PM, Anonymous Anonymous said…

    thanks very much for the instructions...very useful and easy to use

     
  • At 1:46 PM, Anonymous Anonymous said…

    Wow what a helpful tip! @Anonymous, you are so right, ESRI online help sucks.

     
  • At 4:50 AM, Anonymous Anonymous said…

    Good comments.. very useful. thanks

     
  • At 10:31 PM, Anonymous Anonymous said…

    Thank you very much. The explanation is really clear and easy to follow :)

     
  • At 4:01 AM, Anonymous SBL GIS said…

    Hi,

    I too agree with your opinion. it's very useful information and easy to understand. Thank you for you valuable information

    Regards

     
  • At 12:15 AM, Anonymous Anonymous said…

    this was useful thanks

     
  • At 1:39 PM, Anonymous Anonymous said…

    It was great! thanks

     
  • At 1:52 AM, Anonymous Anonymous said…

    That's great, very helpful. Thanks.

     
  • At 11:15 AM, Anonymous Anonymous said…

    Thank, super useful!

     
  • At 1:30 AM, Blogger hilde said…

    OMG, solved my long lasting problem in no time!
    Thanks

     
  • At 10:41 PM, Blogger shylaja said…

    very useful, thanks.

     
  • At 11:15 AM, Anonymous Anonymous said…

    Thanks so much! Us two GIS newbies couldn't figure this out. You are a life saver!

     
  • At 9:09 PM, Anonymous Anonymous said…

    Thank you so much from North Delta GIS er!

     
  • At 3:10 PM, Anonymous Anonymous said…

    when getting control points off a topographic map and putting them in a table is it appropriate to use a legend? Does anyone know when map attributes in such a map affect the usefulness of a legend.

     
  • At 4:02 PM, Anonymous Anonymous said…

    Thank you... that was very helpful!

     
  • At 5:29 AM, Anonymous Anonymous said…

    Unlike the mystification practiced by the ESRI and their useless help files, your explanation is right on. I have been doing GIS for 20 years and do georeferencing rarely and your explanation was enough detail to make me remember how to do it. ESRI should hire you as their help file guru. No kidding. If ESRI doesn't stop this mystification foolishness, they will put themselves out of business because only well paid consultants will know the temple secrets for which they will charge more money than the rest of us can afford. Thanks again.

     
  • At 8:31 AM, Blogger Lisa McLaughlin said…

    Is there a good way to get this done with contour maps? As in georeferencing a hand drawn contour map, then vectorizing the contours?

     
  • At 3:36 PM, Blogger pax61 said…

    This is helpful, but you should add that the image needs to be initially loaded through the "Add Data" button, not the "Insert picture" menu item. Perhaps that's taken for granted by most of your users, but it's not clear, and it took some stumbling around before finding the right way to execute your instructions.

     
  • At 1:14 AM, Anonymous Anonymous said…

    how can i A Extracting Information from Google earth (images) to rcGIS 10

     
  • At 5:46 AM, Anonymous Anonymous said…

    Thanks... though at the end have data going to the C: thus ending the session.

    Files used SID files from David Gurnsey's map collection.

     

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