Difference between UTM Zone 15N and UTM Zone 15T

Question

I'm working on a project where the deliverable is a spreadsheet of point locations and needs to include Eastings and Northings in UTM Zone 15T. I usually use EPSG:26915 NAD83 / UTM zone 15N in this study area, so I was confused about the 15T. I did a little bit of reading about UTM Zones and see that N just means Northern Hemisphere, and that T is a division of the zone above 40 degrees latitude.

If I use EPSG:26915 when calculating the Eastings and Northings will my values be correct for the specified UTM Zone 15T coordinate system?

I'm assuming this is correct but seek confirmation.

Answer 1

Short answer: No, UTM Zone 15 N is not the same as UTM Zone 15 T.

Long answer:

UTM Zone 15 N means the area bounded by:

• east-west boundaries are the longitudes 90° W to 96° W
• north-south boundaries are the equator and latitude 84° N

UTM Zone 15 T means the area bounded by:

• east-west boundaries are the longitudes 90° W to 96° W (the same as UTM Zone 15 N)
• north-south boundaries are latitudes 40° N and 48° N

As you can see, UTM Zone 15 T is 40° of latitude further north than UTM Zone 15 N.

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UTM Zone 15T is actually a MGRS (Military Grid Reference System) "grid zone designator." The MGRS system uses the same east-west divisions as UTM. Each UTM zone is further divided, as explained below:

Each UTM zone is divided into 20 latitude bands, each 8° tall (except ‘X’ is 12° tall), lettered from ‘C’ at 80°S to ‘X’ at 84°N (omitting ‘I’ and ‘O’), so that the zone and the latitude band together make a ‘grid zone designator’ (GZD).

Each ‘GZD’ is divided into 100km squares, identified by a letter-pair (see illustration). Eastings and northings are then given in metres within each 100km square. (source)

So MGRS coordinates end up looking like this: 31U CT 03760 87415, or sometimes the spaces are removed so it looks like this: 31UCT0376087415

• 31U is the grid zone,
• CT is the 100km square within the grid zone
• 03760 (the first half of the numbers following the letter-pair) is the easting
• 87415 (the last half of the numbers following the letter-pair) is the northing

The two-letter grid zones for grid zone designator 15T look like this:

(source)

What is unclear from your description, is whether the easting and northing should be using the MGRS coordinate system, or the UTM system:

1. In the MGRS coordinate system, as measurements from the origin of each two-letter square.

   If they want the coordinates collected in MGRS, it's probably easiest for you to collect the coordinates in a geographic coordinate system (IE as latitude and longitude), then convert then using a separate converter tool.

   • This lat/long to MGRS converter lets you convert one point at a time
   • This lat/long to MGRS converter lets you upload a spreadsheet

-or-

2. In a hybrid of the UTM and MGRS systems, as measurements from the origin of Zone 15 T

   If they want the coordinates collected this way,

   • Measure your eastings in UTM zone 15 N.
   • Measure your northings in UTM zone 15 N, then subtract the distance (in meters or feet, whichever you're using) between the equator and 40°N.

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Note: Before you proceed very far with your data collection, I highly recommend testing out your coordinate collection and conversion method. Use your method to find the coordinates of a known point, then use one of the linked conversion tools to convert it to lat/long. Paste the lat/long in Google Maps (or similar tool) and make the location is correct.