Degrees-Minutes-Seconds, Decimal Degrees, and Eastings and Northings

I’ve worked on two different multi-state fertilizer trials this year. Typically for these types of projects, collaborators from many different labs agree to all apply the same treatments, take the same measurements, and submit data to a single person to analyze and publish. I get the weirdly satisfying (and occasionally frustrating) job of formatting the data in a uniform way.

To make this easier, we send each collaborator a spreadsheet that has a spot for all the information we need to analyze the data. Collaborators just fill out the spreadsheet with their own data in the listed units and send it back to the lab organizing the data.

This system works really well for most types of data. Sometimes collaborators will provide data in different units than the form requests, but they consistently make a note of what units they did use so that we can easily convert it into the units used by other sites.

The one exception is with latitude and longitude. Collaborators consistently provide their locations in degrees-minutes-seconds when we ask for GPS coordinates in decimal degrees. This year I learned that there is a subset of folks who thought that if you include tenths or hundredths of a second in degrees-minutes-seconds format, that means it’s in decimal degrees. This blog post is to clarify the different formats for coordinates and provide some resources for converting between them.

There are three main formats: degrees-minutes-seconds, decimal degrees, and easting and northing. In degrees-minutes-seconds format, the coordinates of Camp Randall is 43°04’06.0″N 89°24’46.4″W. Each degree is subdivided into 60 minutes, and each minute is subdivided into 60 seconds. So, to get 43°04’06.0″N into decimal degrees format, you take 43 + (4/60) + (6/3600) = 43.06833° N. Using the same method to convert the longitude, you get 89.41289° W. NOAA has a great conversion tool if you don’t want to convert these by hand. This one is more basic but also good.

Eastings and northings are less commonly used, but for some spatial analysis they’re helpful. Eastings and northings are based off of the Universal Transverse Mercator map projection (learn about projections here), which divides the globe into 60 zones. The center meridian (vertical line of longitude) of each zone has an easting of 500,000 meters, and the equator always has a northing of 10,000,000 meters. For each meter you travel north of the equator or east of the meridian, you increase your northing and easting by one meter, respectively. The easting and northing for Camp Randall is 303543.38 E, 4771228.45 N within zone 16T. I usually use this converter.

I strongly prefer getting data in decimal degrees because there are fewer things to clean– I don’t have to make sure all the spaces between the degree symbol and the number of minutes have been deleted, and I don’t have to make sure that single-digit minutes have a zero in front. There aren’t any zones to worry about. These are small things, but they become really important when you’re asking a computer to read and map a bunch of coordinates all at once.

I love working with collaborators, and I’m generally happy to go through the process of organizing the data. With these conversion tips, you’re ready to format GPS coordinates in a uniform fashion for your own projects!

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