[GIS] Difference between UTM Zone 15N and UTM Zone 15T

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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.

My question: 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 would love to have confirmation!

Best Answer

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

enter image description here

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

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:

enter image description here (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.

-or-

  1. 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.

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.

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