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MVTA has an ongoing project to map our local trails
using hand held Global Positioning System (GPS) receivers.
This page provides guidelines to help you collect
consistent, usable data for our map database. These guidelines are generalized
for use by anyone with a GPS unit and will assure that the data you collect
will download correctly to the mapping software.
For an overview of how the collected GPS data is
used, see our Trail Inventory page.
 Mapping Software. MVTA owns a copy
of the National Geographic "TOPO!" software and also
has use of the 3D TopoQuads system
by DeLorme. These software packages can display our trails superimposed on USGS
topographic maps. 
Although these maps don’t always show the most
current street info, the basic topographic information is very accurate. This
software can exchange data with most of the commercially available GPS
receivers. If you have technical questions, contact our
webmaster.
Which trails need mapping? Progress is being
tracked via the software systems described above. The trails that need GPS data
are listed on a project database. We can match you up with a trail in your
area. Or you may know of a trail that is not yet in our list. So much the
better!
How to Collect GPS Data for a Trail
Step 1. Before you set out
Batteries – Make sure you have fresh
batteries. Hand held units consume from 2 to 4 AA batteries within 10 to 36 hrs
of continuous use. Check the battery indicator on your unit; replace the
batteries if need be. And carry spares, just in case. You don’t have to
worry about loosing stored data in the unit when changing batteries. It will
pick up where you left off.
GPS Memory – Check that you have sufficient
storage capacity in the GPS memory for the trail you are about to encounter.
Most units will automatically record over the oldest data stored in the memory.
Your unit may offer more options for managing memory. The memory size of GPS
units vary as to the number of waypoints, routes, fixes per route, and tracks.
If you have tracks already stored that you don't wish to lose, you can download
them to a computer to make space for the new trip.
Map Datums and Coordinates – Since we are
using mapping software, the settings you use are not critical. For the purpose
of consistency, we would prefer to collect using UTM coordinates for
CONUS and using the NAD 83 datum. These defaults can be set into
your GPS unit before you start. However, changing these settings afterward will
automatically convert your recorded track information to the default.
Scale – Set the scale of the map shown on
the view screen of your GPS receiver to suit your needs while on the trail. The
viewing scale you choose will not affect the accuracy of the track being
recorded by the unit.
Pack a Notebook - Take paper and pencil with you
so you can make notes as you go: fences, trail conditions, vistas, friendly
property owners (or otherwise), domestic/wild animals, noteworthy flora, and
other landmarks that might help describe the trail. Your notes about the
trailhead, how to get there, and the trail name will be roundly appreciated.
(Many of the trails don’t have names yet, so be creative and make one up,
or it will be given a boring number, until it’s named.)
The notebook is also handy for identifying any waypoints
you may store while on the trail. Waypoints are stored separately from the
track you will be creating. Your unit will give each new waypoint a number.
Note the number and add your notes on paper. (Your unit lets you replace the
number with a short name, but the process is tedious and hardly worth your time
on the trail.) When your track information is downloaded, your notes can be
married up with the waypoint numbers.
Think Safety! – Take plenty of water,
practice the buddy system, and let someone know where you are going and when
you expect to return.
Step 2. Collecting trail data
Your Initial Fix. – Turn the GPS on at the
trailhead before you set out and stay put until you have your trailhead
position established within 20 feet or better. Your unit will need to track at
least three satellites, four to achieve its best accuracy of 15 feet.
Turn on Tracking. – To make the task of
collecting trail data easiest for you, set your GPS to the "Tracking", or
"Breadcrumb" mode when you are ready set out. In this mode, the GPS receiver
will automatically track your trail. You can set the frequency of the points by
distance or by time. Use a minimum distance interval for best results if your
trail makes numerous turns, such as switchbacks. For most GPS receivers, the
shortest interval is 0.01 miles (one breadcrumb fix about every 50 feet.)
Start your trip. – Be aware of the antenna
located in the GPS receiver you are using. The receiver can only function when
the antenna can "see" multiple satellites. If the unit is in a shirt pocket,
backpack, or attached to your belt, it may fail to track properly for lengthy
periods. If at all possible, carry the unit in your hand while on the trail,
holding it away from your body to give it the best view of the sky.
Enroute – As you proceed on the trail, use
your GPS receiver and notebook to record landmarks as waypoints that will help
us to map prominent points, such as forks in the trail, hazards, creeks, roads
or fences. If you return via the same trail course, leave the GPS on and
tracking. The duplicate track will provide corroborating data. Because of the
random inaccuracies of either track version, the combination of the two will
help determine the actual location of the trail when plotting its course on the
topo map.
At the end of the trail – At your
destination, add a waypoint fix and turn off the breadcrumb tracking. If the
trail makes a complete round trip, the fix at the end will serve as a
cross-check for your initial trailhead fix.
Note: If you plan to use the GPS
again before the data is downloaded, keep the tracking feature turned off or
else save the data as a named track within your GPS. That way, your valuable
trail data will not be overwritten by more recent tracking use.
Step 3. Download your trail data
If you don’t have mapping software –
Most folks do not have mapping software available of their own. If such is the
case, contact our
webmaster, who
will gladly arrange to borrow your unit long enough to perform the download for
you.
If you DO have mapping software – Connect
the GPS to your computer and download the track and waypoints you created.
Using the export features of your software, you can create a text file (or set
of files) that contain the fix information. Email these files, along with your
notes that refer to the waypoints by number, to the project leader or
webmaster. |
