# Are ArcGIS' UTM zone designations simplified?

I was recently given a document showing the UTM zones as they appear over the whole Earth. Each zone is 6 degrees longitude by 8 degrees latitude. A numbering system proceeds from 1 to 60 from -180 degrees longitude eastwards, and a lettering system proceeds northward from "C" at -80 degrees latitude. All of this is familiar to me.

In ArcGIS, UTM zones are given with the same numbering system based on longitude, but appear to have done away with the latitudinal lettering system, instead using just "N" or "S", meaning North or South of the Equator. Was this simply done to reduce the number of options users would have to trawl through, or is there a more theory-driven line of reasoning here? Are we losing accuracy by doing away with those zone subdivisions?

• No, I think your're confusing some sort of grid for a UTM zone. The N and S refer to North and South which have slightly different false northings to keep the numbers reasonable. Accuracy is inherent in the storage medium (number of decimal places) not in the projection itself. Sep 14, 2015 at 22:00

## 1 Answer

There are a number of gridding systems which start with UTM zones (which are just the 6 degree bands from the South Pole to the North Pole). The Military Grid Reference System (MGRS) is probably the most famous, and the NGA web site description helps to show how UTM zones are sliced into letters, then map grid designators.

Taken from the NGA site, this is Figure 1 ("60 UTM Zones divided North and South"):

And this is a summary of the MGRS reference grid ("Figure 5. Military Grid Reference System (MGRS)"), which probably looks pretty familiar:

But MGRS continues to drill down beyond NNa naming ("Figure 6. Military Grid Reference System (MGRS)"):

So, in summary, Esri didn't alter the definition of UTM zones, you've just been using a "grid zone" extension and didn't realize it.

• Nice diagrams Vince, that explains it well. I'd seen these grid designations before on aviation navigation maps but didn't know who came up with the spec.. Sep 14, 2015 at 22:45
• I learned MGRS as a ROTC cadet in the 80s, but the Defense Mapping Agency (DMA) created it long before then. Sep 14, 2015 at 23:24