Finding Your Way with the Universal Transverse Mercator (UTM) System
and Why It's Easier than Latitude/Longitude
If you have ever been confused by the lat/long system on your topo map, you are probably going to embrace the much easier system of UTM. The lat/long method uses minutes and seconds to mark coordinates on a map that is a tall rectangle rather than a square (the Earth is not actually round; the polar circumference is greater, by a small amount, than the equatorial circumference) so 7.5 minutes North and South is a different distance than 7.5 minutes East or West. Now let's immediately look at the Universal Transverse Mercator System, better called simply UTM.
UTM is based on easy-to-visualize “squares” of 100 meters on each side (these are still not exactly square, but close enough! Read on...). The Earth's surface is divided into a set of East to West sections (zones), like segments of an orange. There are 60 UTM zones, each zone segment is a region defined by the area between two longitudinal lines that are six degrees wide. The same type of grid is used from the Equator to both North and South. The resulting squares are then subdivided into 10-meter chunks. Every topo map is marked along the edges with blue tick marks to show the UTM grid. (Here is an excellent in-depth explanation...)
The Global Positioning System (GPS): Finding the Treasure
GPS? More alphabet soup? Yes, but the acronyms are over. GPS units are used to receive signals from satellites and convert the readings into ... UTM coordinates. This is “X marks the spot!” taken to the hi-tech extreme. If you have not yet realized what GPS is about or how it can work for you, read on:
A waypoint is a specific X-Y coordinate for a place on the map. Coordinates can be in latitude/longitude, or the much easier UTM style. A waypoint can be anything important: a favorite camp spot, highway intersection, Aunt Sue's house. You can find these coordinates by searching on place names at TopoZone.com or the USGS Geographic Names Information System. Once you find a place and get its x-y coordinates, just manually enter them into your GPS unit and save with a destination name.
For starters, imagine this: you enter a bit of data called a waypoint into a small GPS unit, then you tell it to lead you there (the GOTO function). The little display puts up a pointer to show you the direction to the destination and constantly updates how far away (by direct line) it is. You may need to wander due to terrain or vegetation, or drive a winding route of highways and byways but the pointer always keeps you aware of the true direction to your goal. Following the pointer lets you know when to turn left or right, and you choose the route that keeps you heading toward the target. Eventually you watch the display count down the remaining distance until you are within as little as 15 feet of the location you wanted.
Note: There used to be a “wobble” built in to the signals to intentionally deliver a slightly less than accurate position, the idea being that bad people couldn't target with precision. In 2000 this wobble was turned off and now most any GPS unit can promise accuracy to within 10 meters or less, some listing three meter accuracy.
Starting in December, 2005 Europe started launching a series of satellites to build a 'constellation' and a navigation system called Galileo (read the BBC website story here) which will soon offer even greater accuracy and added features that will interest any avid GPS users who tend to wander far afield.
Welcome to GPS 101
As was just mentioned, GPS relies on signals from a specific network of satellites in geosynchronous orbits. They each send out a signal every second, each using a unique code that is received by any GPS unit. The GPS understands which satellites it "hears" and can compute the time it took for the signal to reach it. When it hears (acquires) at least three satellites it can triangulate and announce the one place on Earth that those signals would intersect: Bingo, you know where you are. It is fast and accurate. From shopping mall parking to hitting the local trails, to heading off for another part of the state, GPS is a terrific tool for so many reasons. Not only can it lead you to a place, it can lead you back home, and it can lead others to a place you want to share, assuming they also have a GPS unit.
So Why is this Useful for Botany?
A few years ago we wanted to go see Mimulus rupicola. I found a few notations in Calflora that indicated a specific location; I set a waypoint and off we went. About 300 miles later, we arrived at the waypoint location: a limestone wall in a road-cut in Death Valley. A little time spent looking around and we found the flowers. A few weeks later somebody else used their GPS with the waypoint, and they too found the spot. Imagine how almost useless it would have been to say, "Drive five miles from the Eureka Dunes turn, then look for the dark limestone wall!" That could have left several options open for discussion, but our friends drove to the right spot.
Another good use would be to mark the location of your car, camp, or whatever, and then go wandering around. Not only does a GPS track how far you have walked and where you need to head to return, you can easily mark waypoints of particular interest and transfer them to maps later to document your finds, just as we did with the Mimulus. You might also mark patches where invasives have taken hold so that you can report locations to the USFS or local native plant groups.
Tip: Do NOT buy any books to explain GPS!
Don't repeat my mistake: keep your money and spend it on an an atlas or some new book about botany. This is really very straight-forward. There are many web pages that all repeat the same stuff and it's free to read that. If you get a GPS unit and read the manual, a Google search will dig up anything that needs clarification. Heck, you could even drop me a note to let me know what kinds of things aren’t coming clear.
A half hour spent walking around your neighborhood with a GPS will tell you most everything you need to know.
The Benchmark Atlases (see Amazon book links below)are very useful books, along with being graphically beautiful: shaded-relief maps with overprinted GPS grids.
And don't buy any plastic grids for topo map use until you have tried mine, for free: TopoGrid.pdf 
Along with your location, you get extra information that relates to your place on the face of the planet: sunset time, sunrise, moon rise and set (and maybe the phase), and probably the elevation. Inexpensive units like the Garmin Geko shown here are adequate for most things, plus so small they fit into a pocket. GPS units have come down from $1000 units 15 years ago to now a few for under $100 and very main-stream. I consider them mandatory for the equipment list usually called the "Ten Essentials"; a GPS makes it 11.
Benchmark Atlas for California
Benchmark Atlas for Washington
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