GPS Basic Info

Note: below is a pdf file that explains some basic set up and downloading operations........

There is a lot confusion pertaining to data transfer and management.  For hiking and location finding purposes, stick with the big four: Maps, Waypoints, POI’s and Tracks.  (I know, there are also routes and custom maps and geocaching, but they are for other uses or for the advanced user.)

Maps are digitally loaded in a gps to be the base topo view.  Some GPS units come pre-loaded with maps (Check your specs.) Most maps are USGS based topo maps of various dates and quality.  Do not assume that the info on the base maps are current.  Trail and roads are often wrong.  Garmin "maps" come in two varieties now, the 24K series and the 100K series.  The 24K series is supposed to have more detail showing only a few states at a time..  The map sets can be loaded directly in to some gps unit's internal memory or they can be loaded onto an SD card.  These "maps" can also be loded into Garmin's BaseCamp program to preview and edit your data.  

Garmin also sells their maps pre-loaded onto an SD card.  This may seem like like a great idea, but I don't advise purchasing the pre-loaded map SD cards.  The pre-loaded Map SD cards may require you to swap the SD card for "in the field loading" of waypoints, etc.(See the Bear Creek web site for this) I just don't like the swapping of the itty-bitty micro/mini SD cards if I don't have to.  Plus the Garmin Pre-loaded SD card maps are not viewable in the BasCamp program on your computer.  There are some third party FREE maps that are available for downloading.  But there quality is variable and may not be supported to load in your gps.  The web site for these maps is:    

GPS File Depot 

Waypoints are the easiest to deal with.  A waypoint is a “point” or spot on the surface of the earth and its location information.  The information consists of the coordinate, elevation, and a description or name of the point, etc.  Waypoints can be pre-loaded INTO the GPS and/or they can be field ADDED during your hike.   Most GPS units have a maximum number of waypoints at around 500 to 2,000 (check your specs).   I like to only add (field mark) waypoints in the field, marking road crossings, water sources, camp spots, etc. for post hike reference.  I therefor tend to load LARGE numbers of pre-hike "waypoint data" into my GPS in the form of POI’s (see below).

POI - Points Of Interest - are simply put, converted waypoints.  GPS units can handle a very large number of POI points and they can be loaded onto the SD card(or internal memory).  Garmin has a free program that converts and loads POI points.  This is possibly just an extra step for most people, but I find it useful. So one great solution is to load thousands of waypoints into the POI file converter program, then load the POI file into your Garmin GPS.  Bear Creek Survey (see Links) now has a loadable POI file with up-to-date files for the entire trail!!!!!!

Track files are lines drawn between data points of a path, a “track.”  Tracks can be loaded to a GPS from files made on a computer or from data collected in the field.  These tracks can be edited and then re-loaded for future use.  (If it was only that simple.)  How tracks are handled by your GPS can vary even within a model family.  Tracks can also be “active” if you leave your GPS turned on showing the path you have just walked.

Warning Number 1:  If you are old enough, you may remember the old days of computer programming.  There was a phrase that was used a lot; GIGO.  GIGO was an acronym for Garbage In Garbage Out.  The data loaded into your GPS is only as good as the data is good.  So, check your data and always know that it could be wrong!  The perfect example is the track files that are being passed around of converted Google Earth trail alignments from sites such as and Jonathon Ley’s web site.  They clearly state that the alignment files are dated and not complete.  Always check any GPS data against the up-to-date Jonathon Ley maps.

Warning Number 2:  Always know what DATUM your data is in and what DATUM your GPS is set in.  The default is WGS 84.  You could also see data in NAD 27, or in NAD83.  Plus, data can be in UTM format which is metric.  Your Lat/Long can also be in digital degrees; or degrees and digital minutes; or degrees, minutes, and seconds.  I use WGS 84 and degrees and digital minutes.


File structure is another factor in handling data.   All GPS manufactures have their own proprietary file structure and extensions.  For instance Garmin files that contain waypoint, routes, and tracks are saved as: filename.gdb.  DeLorme is:  filename.gpl.  There is now a standard file format that is being used by most GPS manufacturers and mapping software programs in the form of: filename.gpx.  Fortunately there are third party programs that help you in conversion of these formats.  My favorite is GPS Babel:

StarMan, this is all very nice, but my head is about to explode……What GPS should I buy and how should I use it?

One OLD option:  A simple system used by “Out Of Order.”  He had the Garmin Colorado 400t with the pre-loaded topo maps.  He then drew out track files of the entire CDT based off of the 2009 Jonathon Ley maps.  The Colorado and Oregon series could handle the “OOO” track files in their full size.  However, this file is now dated and does not reflect the official CDNST alignment.  I would not use this file and instead would use the new Bear Creek files and the alternates posted on their site.

UPDATE:  I have purchased and started using the new Etrex 20.  Bottom line is I suggest you just purchase this unit. 
I am finding the Etrex20 to do a pretty good job in the field.

You can also have a very basic unit that only tells you the Lat/Long and use the GPS Compass Rose method explained on Jonathon Ley’s web site or just refer to topo maps with Lat/Long tick marks for reference.

A new option or method uses Apps loaded on a smart phone or even tablet.  Once again, I would NOT trust my life on a phone App alone.  (Do I have to mention a map and compass again)

No one answer, no one way to do it.  If you are a geek like me and love to read manuals and have long chats with tech support, then a GPS can be fun, interesting, and a challenge only in its limits.  If you still have a VCR that is blinking 12:00, then I would suggest keeping it simple and practicing a lot prior to your trek.  If you don't know what a VCR is.....well, you are probably ok!

Warning Number 3:  Do NOT use a GPS as your only or primary source of navigation.  Have up-to-date maps and a compass.  GPS is both a toy and a tool.  For me, it is ONLY a back-up to my maps, compass  and my common sense “trail-smarts.”  PLEASE print and carry the Jonathan Ley maps and/or the Bear Creek Survey CDNST Map Atlas......

Note: below is a pdf file that explains some basic set up and downloading operations........

Frank Gilliland,
Feb 23, 2015, 9:12 AM