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)
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?
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.
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
