Instructions for Geo-Registering Maps in ArcView

 

***Before you begin, make sure that the following extensions are loaded:

1^st_tools; Image Analysis; JPEG

Also, say “yes” to any prompt asking you if you would like to have pyramids built. Though this takes a long time, it speeds up the process later on immeasurably. Please also use a computer with a large amount of available disk space, as the finished product can require over 300 megs of disk space.

 

1.      Get the latitude and longitude coordinates from the maps you are using. Try to choose spots as close to the corners of the map as possible, but make sure that the points align to a square. Enter these data into attribute tables (a separate table for each map) in decimal degrees*. Remember that West Longitude and South Latitude must have ‘-‘ signs before them. Longitude is the x-coordinate, latitude is the y-coordinate.

*Forgot how to convert to decimal degrees? Use this formula:

decimal degrees = degrees + (minutes/60) + (seconds/3600)

 

Create a new view or use your scratch view for the next few steps.

 

2.      Add an event theme – pick the table you created for this map.

 

3.      Set view properties for this view to the appropriate projection (in the case of British railway maps, National Grid/Great Britain).

 

4.      Convert the event theme to a shapefile, and add this shapefile to the view.

 

5.      Make this theme/shapefile active, then right click on one of its dots and choose 1^st_tools from the menu.

 

6.      Click the top right button on the window that opens: it is called ‘add XY coords to FTAB’

 

7.      Open a new view and add an image theme of the appropriate map.

 

8.      Choose the ‘align’ tool.               While using this tool, locate the coordinates you typed into the attribute table on the map image. Left click on the appropriate spot, then right click and choose ‘enter TO coordinates’ from the menu that appears. When the dialogue box opens, enter the X and Y coordinates that ArcView created on step six. You can leave out the numbers after the decimal point.

 

9.      Choose the 'theme' menu and 'save image.' Say 'yes' to the dialogue box that asks if you want to save the control points. Though both *.img and *.tif files are rather large, if disk space is a problem choose *.tif.

 

 

 

Trouble-shooting tips:

v     When you open your project at a later date, you may get an error saying ‘warning, project ______ could not be opened.’ If this happens, ignore it. Click ok, let ArcView finish loading, and then open the project from within ArcView.

v     If a dot shows up in the wrong place on step 8, select it with the select tool, then choose the align tool, right click on it, and choose ‘delete selected link’ from the menu that appears.

v     Your image may change shape drastically, mirror itself, turn into a thin ribbon, flip upside down, etc. This is normal and should not be a cause of concern. If it happens, it is a result of either a misplaced dot or wrongly entered coordinates. Delete the links you have made and start over. This can be done as mentioned in the step above. If the transformation only happened on the last of the four links, right-click, and choose "pan to worst link" and delete and re-enter that one to see if it worked.

v     For the sake of consistency and ease of memory, always enter your data and work in general in the following order:

 

 

 

 

 

 

 

 

Compiled by Jon Caris and Mikaila Arthur, 2001.