GIS/GPS – converting coordinates

Converting Written Coordinates

Sometimes, especially with recreational hand held GPS units, it is easier to simply write down the coordinates. If this is the case, you’ll need to do some work to get them viewable in GIS software.

First you need to convert your latitude/longitude or UTM to decimal degrees. You can either do this by hand (for lat/long) or use an online converter.

By Hand:

Ex: 28 degrees, 22’36” -107 degrees, 01’14”. The equation that you need to use is: degrees.min/60 + sec/3600.

So in our example, we would divide 22/60+36/3600=.3766. The final answer is: 28.3766 (Y) and -107.0055 (X). Keep in mind that in our area, X is ALWAYS negative (e.g. -107, -106).

Online converter:

Lat/Long to decimal degrees, <a href=”http://transition.fcc.gov/mb/audio/bickel/DDDMMSS-decimal.html”>click here.

UTM to Lat/Long (then use the above converter to go to decimal degrees), <a href=”http://home.hiwaay.net/~taylorc/toolbox/geography/geoutm.html”>click here.

Next you’ll need to open Notepad. You should enter the decimal degrees so that they look like this:

X,Y

-107.0055, 28.3766

-107.1122, 28.5679

Save as a .txt file.

Open ArcMap

Hit the add data button

Add the .txt file

Rt click the file and choose Display X,Y Data

Then Right click the data, and choose Data, Export, and choose to export it as a shapefile (.shp).

When it asks you if you want to add the new file into the map, say yes. It will read in decimal degrees, but show the lat/long

Then open the toolbox, Data Management, Projections and Transformations

Define projection

Choose your new shapefile

Click on the tab next to coordinate system

Choose select

Select the appropriate projection.

Keep in mind that if you define the file incorrectly, it will display incorrectly.

The file needs to be correctly defined before it is reprojected.