How do I scan a hardcopy map so I can use it in ArcGIS?

The basic process is to scan the hardcopy map, save it in an image format readable by ArcGIS and then register/rectify the scanned image. There are a variety of ways to scan hardcopy sources on campus, including large format scanners (Fine Arts) and letter-sized (many STC's have scanning capabilities including the Mac lab in Student Building 220 and the central computing staff station on the second floor of the Student Building).

The following are the basic steps to scanning a map in the Student Building Mac lab:

1) start Photoshop (Apple Menu : Graphics)
2) Select File : Import : Silverast (Epson)
3) Click Prescan and then adjust the scan area by dragging the box handles in the scan window to include the area of your hardcopy map you want to scan
4) Set the scan type (grayscale, color depth) and resolution (dpi)
5) Click Scan
6) Rotate image in photoshop if necessary
7) File : Save As - and then save image as a jpg or tif file - Note, there are many image file formats, the main thing to keep in mind is that you want the image to be in a format that ArcMap can read so that the file can be used as a source to generate a registered/rectified image. TIF files and JPG files (at least the current incarnation of the JPG format) do allow for this type of processing.
8) You can save the image to your CFS space on the Mac. Here are instructions on how to mount your CFS space from the Macs.

Then you can add this jpg or tiff image as a data layer in ArcMap and rectify it to another layer in a specified spatial reference system. The general steps to georeference this dataset are as follows:

1) Add the base map product which you will use to supply the map coordinates to your ArcMap session.

The base map can be any map product that has is in a specified spatial reference system (coordinate system, map projection, datum) and contains features that are observable on the image to be registered/rectified (i.e. road interesections).

2) Add the scanned image file which you want to georeference to your ArcMap session.

2) Add the Georeferencing toolbar - From the main ArcMap menu select View : Toolbars : Georeferencing

3) Iteratively select a point location in the scanned map (which is in file coordinates (i.e. not in any map coordinate system)), then select the matching point location in the base map (which is in map coordinates) until you capture a minimum of four points. You will need to turn on and off each of the map layers so that you are able to see the layer from which you want to capture a point. Also, you will likely need to Zoom to Layer (right-click on layer in table of contents) to get to the correct extent for the first few points. After you capture a few points ArcMap will overlay the two layers onto the same general coordinate space. If you ever have problems in the middle of a selecting a pair of file/map coordinates you can press the Esc key to start over for that point.

4) Assess the aggregate RMS error associated with all points and the contribution of each point to the RMS error. Delete and re-capture points if necessary. The desirable RMS error is a product of the scale of the base map and the resolution at which you scanned the map to be registered/rectified. NOTE: While there is no mention of this in the ArcGIS Desktop Help that I could find (v. 8.2.1), the ArcMap Georeferencing utility reports RMS in map units (i.e. if the RMS error is 1.3, that means 1.3 meters, not 1.3 cell units).

• The right hand icon (looks like a small table) you can view the coordinate pairs for the source (un-georeferenced) dataset and the dataset in Map coordinates. After you have completed four registration points (for which you have both a file and map coordinate) you will see the contribution of each individual point to the overall RMS error. You can delete registration points and redo them by left clicking on the registration point row in the table and then clicking the "X" icon/button on the right side of the dialog box. This is helpful for times when you make choose the wrong location for the file coordinate or map coordination by mistake.

5. Once you are satisfied with the registration and RMS error, rectify the map: Select "rectify" from the Georeferencing toolbar, fill in the filesystem location and name of the rectified output dataset you want to create and click "Ok". This will produce a Grid raster dataset.

6. The last step is to define the spatial reference information for the newly created, rectified data. (note, this step may not be necessary, you can check the metadata for your georeferenced dataset in ArcCatalog to confirm whether you need to

• In ArcToolbox go to Data Management Tools : Projections and Transformations : Define Projection
• Insert the newly georefenced dataset in the "Input Dataset or Feature Class" field
• Click the icon to the right of the "Coordindate System" field
• Now you can either manually set the spatial reference information by choosing the "Select" button, or you can grab the spatial reference information from another dataset to be used to supply the spatial reference header information in your newly georeferenced dataset by choosing the "Import" button.
• Click Ok to finish.

The ArcGIS help includes pretty good instructions for using this utility. In the ArcGIS Desktop Help find the item in the Index (click the "Index" tab under the Help menu) listed under "georeferincing, raster dataset ". You should also refer to the conceptual discussion of registration and rectification in the main text.