Digitizing paper-maps in ArcView

contact: rbrand@mail.utexas.edu

General Help can be found in the ArcView manual p. 281-291, in the built-in ArcView Help and in the Image Analyst manual p. 99 ff. General ArcView tips are available at: http://mather.ar.utexas.edu/Courses/parmenter/gis/tips/index.html

Two  Possibilities to digitize paper-maps:

1. Using the digitizer tablet

2. Tracing lines or points of a scanned image directly on the screen

1) Using the digitizer tablet

• Prepare the map: Specify at least four control points whose exact coordinates you know (i.e. select coordinate system tick marks along the margins of the map.) Mark them with a pencil and assign a number to each. Calculate their coordinates in decimal degrees. For example 90° 45'  =  90.75. Pay attention that locations west of the 0 meridian are negative. Fix the map to the tablet with a masking tape.

• Turn on the digitizer tablet

• Restart the computer (when you are asked for a password, you don't need one - just hit Enter)

• Open CalComp (Start / Programs / CalComp) to assign certain functions to the puck's buttons. Ensure that you have at least specified one button each for "left", "left double", "right" and "middle double" click.

• Open ArcView (click  on cancel in the very first dialog)

• Activate the Digitizer Extension (File / Extensions: checkmark Digitizer)

• Create a new View and specify its properties (View / Properties). The Projection in our case it's mostly "UTM" - "zone 14". Click OK and specify the Distance Units to "meters". Click OK

Digitizer Setup (View / Digitizer Setup)

The dialog should show one dark line awaiting the 1st control point

• Highlight the puck icon

• Set units to "decimal degrees"

• Click once on the puck with the button that was specified before as the left-click (see above under CalComp) and move the puck over the tablet. The puck can function in two different modes:

1. Relative mode: If you move the puck the cursor works like the mouse

2. Absolute mode: If you move the puck the cursor works like a digitizer and is "caught" within the view-window.

Remember: You can always switch between these two modes by pressing F2!

• At this stage you need the puck in the absolute mode.

• Click (with the left-click-button) once exactly at the first control point of the paper map. Click once at the second point, at the third point etc. until you have at least four control points.

• Use the real mouse again, click in the field for the X-value of the first control point and type in the exact coordinates for each control point (in decimal degrees !!).

• If you did everything well the calculated error should be below the default value of 0.004 in. If so, save these points for further digitize-sessions in the project-folder and then click on register. If the calculated error is above the acceptable range (default - 0.004 in) redigitize some or all control points. (By the way: the reference points and lines in the "geo-....shp" files are digitized with an error of 0.0017 in)

• Create a new theme (View / Create a new theme) chose a theme-type ("point", "line" or "polygon") and specify the path and the filename for it.

• Use the puck in the relative mode (maybe you need to press F2)

• Zoom in to your area of interest by following these steps:

a)  click with the puck (in the relative mode!) on the Zoom-in Icon

(= symbol for the magnifier glass with the plus sign)

b)  Use the puck in the absolute mode

c)  Click (left-button) with the puck a little left and a little below the bottom-left corner of your area of interest of the paper map.

d)  Click (left-button) with the puck a little right and above the top-right corner of your area of interest of the paper map.

• Now you need the relative mode of the puck again

• Click with the left-click-button of the puck on the drawing tool you need (see examples on the right)

• Go to the absolute mode

• Finally: Digitize and enjoy it. If you are drawing a line or a polygon your last point has to be a left-double-click (whatever button you have specified to this function).

• Go to the relative mode

• Theme / Stop editing and save your new file.

• If you want to create another theme start again with View / Create a new theme

Here comes the bad news: If some georeferenced points, lines or polygon within your area of interest already exist (maybe from other members of a project-team), you wouldn't have to go through this tablet-digitizing process. In that case you could simply use the second possibility which is described below.

2) Tracing lines or points of a scanned image directly on the screen

Scan your map by following these steps:

• Go to a Macintosh Computer that is hooked up to a scanner. Open Photoshop (Apple-Symbol / Applications / Photoshop)

• Click on File / Import / Scannername

• Click on Preview, wait, and then resize the little rectangle (the one with the walking ants) over your area of interest.

• Specify whatever you want. Some rules of thumb are:  

reflective mode, resolution = 300 dpi, color=24 bit RGB

• Click on Scan and wait

• Save the image in the "TIFF" file format and if asked for a computer type chose "IBM PC"

• Close Photoshop

• Open Fetch (Apple-Symbol / Networking / Fetch)

• Type in the host-line: "mather.ar.utexas.edu"

Username = anonymous, Password = your@emailaddress

• Specify the target folder (normally "\pub\temp")

• Click on Put, double-click on the file you want to transfer, chose "raw data" and click OK

• Wait until file transfer is complete and close Fetch

• Go to a PC

• Open WS_FTP (Start / Networking / WS_FTP)

(Help for FTP is available at    http://www.utexas.edu/cc/training/handouts/wsftp.html/ )

• Connect to "mather.ar.utexas.edu".

Username = anonymous, Password = your@emailaddress

• Specify the target folder in your local system (= left part of the window)

• Go to the source folder in the remote system (= right part of the window)

• Since you want to transfer an image click on Binary

(the middle toggle at the bottom)

• Click on the arrow from right to left in the middle  and wait until transfer is complete.

• Close the connection and Exit

• Open ArcView

• Open the project with the already georeferenced shape-files in it (e.g. the shape-files you have created before with the digitizer tablet)

• Activate the "Image Analyst Extension" (File / Extensions. checkmark "Image Analyst")

• Add a theme (View / Add a theme), chose "Image Analyst File" as file type and go along the path to the scanned TIFF file. Highlight it and open it.

• Make the new TIFF-Image visible (that is, checkmark it) and move it to the bottom of all your layers (just drag and drop)

• Zoom in to the area where the new TIFF-Image should appear.

• Activate the theme with the TIFF-Image (just click on it once)

• Click the Align Tool once and be surprised!