Tone Ag Consulting Ltd.

When you’re mapping a curved surface (like the Earth) onto a flat one (like a piece of paper), you need to use a Map Projection.  There are many, many map projections out there and often you’ll find that some of your data is in one projection and the rest of it is in another.  The easiest way to convert all your data to one projection is to use a map projection utility.

I use Arcview 3.2a for most of my GIS work.  It comes with a external projection utility program with the clever name of Projection Utility.  It’s pretty straightforward to use.  Usually I need to convert data from decimal degrees to UTM, so here are the steps I follow on Windows XP:

1. Start/Programs/ESRI/ArcView GIS 3.2a/Projection Utility
2. Press Browse and find the shapefile(s) you want to convert, Press Open, Press Next
3. Choose the current coordinate system for your shapefile(s) (For me it’s usually Geographic, GCS_WGS_1984 [4326], Degree [9102]), press Next
4. Press No for saving the coordinate system  if it asks
5. Choose the new coordinate system for your shapefile(s) (I usually use Projected/WGS_1984_UTM_Zone_14N [32614], Meter [9001]), press Next
6. Select the target directory, press Next
7. Press Finish
8. It’ll chug away for a bit and you’re done!

Unfortunately every once in a while I run across a file that doesn’t want to process properly. I’ve found another projection utility that seems to handle errors better. It’s a command line utility, so here’s what I’ve come up with for running it from Windows Explorer.  WARNING: This method will overwrite existing shapefiles with the new projection.  Backup your files first!

1. Download SHPTRANS: Shapefile Coordinate Transformation Utility
2. Run the setup program.  It will create a directory called C:\SHPTRANS
3. Create a new file in C:\SHPTRANS, SHPTRAN.BAT
4. Edit that file and put in the line
   C:\SHPTRANS\shptrans.exe %1 -inplace -from=GEO,NAD83 -to=UTM14,NAD83
5. You may need to edit that line.  See the readme.txt file for your from and to parameters.  This one converts from geographic NAD83 to UTM Zone 14 NAD83
6. Save and exit
7. In Windows Explorer right click and choose Open With for a .shp file.  Browse to C:\SHPTRANS\SHPTRAN.BAT.  Press Okay.
8. Right click on shapefiles (one at a time), ch0ose Open With/shptran and you’re good to go!  (Alternately choose Always use selected program to open this kind of file and you can just double-click on a shapefile to convert it. Much more potential for destruction this way though.)

It’s not terribly elegant, but it works.  REMINDER: This will replace the existing shapefile with your new projection.  If something goes wrong your file may be destroyed.  Back it up first!