Grid System for Sandia Mountains   (ver 2)
Goal: The purpose of this grid system is to provide unique names for a locations in the Sandia Mountains. Each name should be 6-characters and contain within the name the actual value of the specified location.

Description of Grid

  • This version of the Sandia Grid System converts Minutes of latitude and longitude to Base32  (see Note A)
  • The 2 character grid prefix designates Minutes of latitude and longitude, and the 4 digit suffix designates fractional minutes (hundredths) of lat/long.
  • Latitude begins at 35°0'n and sequences northward through 35°31'.
  • Longitude begins at 106°0'w and sequences westward through 106°31'.
  • Format for point names is lat-grid-label, lon-grid-label, hundredth_minute-of-latitude, hundredth_minute-of-longitude.  (see Note B)
  • Example: The Pino Trailhead is labeled 9w8022. This point is at lat grid 9 (35°9'n) & lon grid W (106°28'w) with decimal minute values of o.80' lat and o.22' lon. Actual coördinate value is 35°9.80'n 106°28.22'w.
  • Although current USGS and USFS maps of this area still refer to North American Datum 1927 (NAD27), the grid and point designations of this grid system are based on WGS84 (NAD83) .  (see Note C)

  • Sandia Grid version 1
    Notes

    A) Base32

  • The Base32 numbering system allows using a single alphanumeric character for numbers from 0-31.
  • This system uses the Hexadecimal codes for 0-15 (0-9,A-F) and the letters G-Z for 16 through 31.
  • Not used are the characters: I L O U. (I & L could be confused with numeral 1, O with zero, and U with the letter V.)
  • Some years back, I wanted a Base32 system to use for dates, allowing a 3-character "number" to indicate year-month-day (which is fine until 2032). I started with the zero thru F hexadecimal (Base16) system and just worked up the alphabet. With more letters than needed to attain 31, I decided to leave out those listed above.
        Subsequent research led me to discover that Douglas Crockford had already developed and published a similar, though superior, system. Thus, while I state that I developed this system independently, I also stress that credit goes to Crockford for the above described Base32 System.

  • Why switch to Base32?
  • The original Sandia Grid system (ver 1) relies on a simple table to decipher the latitude and longitude values. Latitude was simple enough. A-Z correspond to the numbers 0-22 (I,L,O aren't used). However, Longitude also uses A-Z, but the values are different, representing instead 15-37. It needed something simpler and more intuitive, thus Base32.
  • Mathematician and songwriter Tom Lehrer stated that Base8 is just like Base10 – if you're missing two fingers. Take that a step further and imagine that your polydactyly has blessed you with 8 digits on each hand and both feet. Consider that you use all those fingers and toes to count to ten: Base32. What could be more intuitive than that?

    B) Accuracy: Seconds vs Decimal Minutes

  • I developed my original version of the Sandia Grid before I'd ever heard of GPS and had grown up with the mindset of Degrees/minutes/seconds. When I later heard about using Degrees and decimal Minutes, it seemed like a strange hybrid which I found aesthetically and logically unappealing. If you want to use decimals, just go with decimal Degrees, which provides a simpler and more accurate measurement.
  • However, I've come to appreciate the merits of decimal Minutes, if for no other reason than they work for a Sandia Grid. Using Minutes, rather than decimal Degrees, provides a handy basis for the grid, and dividing those Minutes by a thousand–or even a hundred–provides a welcome accuracy increase. Accuracy for a Second of Latitude is ±31m. Oppose this with one thousandth of a Minute which is ±2m. Even using hundredths of a Minute increases accuracy by 66% over using Seconds.
  • Although most GPS receivers indicate decimal Minutes to thousandths (.oo1), designating SG point names to hundredths (.o1) allows an accuracy of ±18m latitude and ±15m longitude (at 35°). This might not be sufficient for treasure hunting, but it's close enough for trailheads, junctions, and parking lots. Dorothy 
and Toto

    C) NAD27 vs NAD83/WGS84

  • The Global Positioning System is based on WGS84, and GPS receivers default to using that datum. (WGS84 is effectively synonymous with NAD83.) To borrow from a Wikipedia article, "the coordinate origin of WGS 84 is meant to be located at the Earth's center of mass; the error is believed to be less than 2 cm." Contrast this with NAD27, for which the coordinate system for the lower 48 is based on a farmhouse in Kansas. Anyone familiar with the Wizard of Oz knows that farmhouses in Kansas are sometimes hard to pin down.
  • Even though the current USGS and USFS maps of this area still refer to North American Datum 1927 (nad27), it seems as though points which will be used primarily with a GPS receiver should reference the NAD83/WGS84 datum.
    MycoWest.net/gps/sa-grid.htm
    dmw . 2o13-o2-o3