Using the Garmin GPSMAP 66 in the Field

I have a GPSMAP 66S, but what I have to say here applies to the 66ST as well- the only difference between the models is that the 6ST adds Garmin Topo maps. I prefer to load my own maps from, which are more detailed than Garmin's 100K maps and are free. So, when I refer to the GPSMAP 66S below, I mean both models.

Before I get started, let me say that the positives in this unit far outweigh the negatives, at least for my use. The core function, that of locking onto satellites and determining your position, is significantly improved over the already excellent GPSMAP 64 series.

First, the negatives- the synchronization feature, which uses the Garmin Connect and Explore smartphone apps to send data from the GPSMAP 66 to and from your phone and the Garmin Explore website, are unnecessarily complex and fiddly. I was hoping for something as simple as Gaia GPS's sync from their phone app to their website, which takes place automatically in the background. All I have to do is record waypoints and tracks with the Gaia app on my Android phone as I hike, and as long as my phone has a data connection at some point, all my data is there on then I log in.

The GPSMAP 66, however, records your track as something it calls an "activity". Activities are not automatically synced to the phone and website, unless they are saved as a track on the GPSMAP 66. Activities are clearly aimed at the fitness market, because that data is recorded in FIT and GPX format by default. However, it adds an unnecessary step if you just want to record a track log. For example, let's say that you want to map a trail. First, you have to make sure the GPSMAP 66 is set to record the activity. For hiking, I've found the best settings are the default, including auto pause (this means recording will stop when you stop, and resume when you start to move again.) As you hike, save waypoints at trail junctions and other important landmarks as usual. Back at the trailhead, go to the Recording Controls page and save the activity. Then go to the the Recorded Activities menu item, open the activity you just saved, and save it as a track.

To get a track log onto your computer, open Garmin Explore, go to Devices, and touch the Sync icon next to the GPSMAP 66s (this assumes you've already paired the 66s with your phone. You'll need the Garmin Connect app to do this.) Now, open on your computer and go to the map tab. After a few minutes, the Library pane on the left synchronizes and you should see all of your data from the GPSMAP 66.

I happen to prefer working with CalTopo ( for trail mapping- I've invested a fair amount of time in learning to use its tools, so I need to export track and waypoint data from Garmin Explore and import it into CalTopo. To export the data you want, you have to set up map filters in Garmin Explore so that only the data you want is shown on the map. Then you can export it as a GPX or KML file. In my case, I export to GPX and import into CalTopo. Whew!

Ir's much easier to do it the old-fashioned way, by connecting the GPSMAP 66 to the computer with a micro USB cable (yes, Garmin's finally stopped using the totally outdated mini USB- now if they'd only gone straight to USB-C. Oh well.) As soon as the receiver senses the connection, it saves all of it's waypoint, track, and route data as GPX files. The internal storage on the unit shows up on your computer as the Garmin drive. Now all you have to do is navigate to the Garmin/GPX folder, and there's the data. Waypoints are saved in a Waypoints file with the current date, and track and route files are date and time stamped (unless you renamed them on the unit while saving them.) Now you can import any of the GPX files directly into your mapping application- any mapping app worth bothering with can import GPX.

It's also easy to import GPX files to the GPSMAP 66. This is useful for trip planning- you can enter and name waypoints and routes much easier on the computer than by using the keypad on the GPS unit. In CalTopo, start a new map (the default when you log in), then create all the waypoints and tracks (shapes in CalTopo)you'd like. Then export to GPX. The export function presents you with a popup dialog with all the data on the map- just check off the items you want to export. The GPX file will have the same name as the current CalTopo map. Then copy the GPX file to the Garmin/GPX folder on the GPSMAP 66.

Even better- use a micro SD card in your GPSMAP 66. If present in the unit when you connect it to your computer, it will show up as a second drive. Any GPX file you copy to the Garmin/GPX folder on the card will be recognized by the unit. This also saves space in the internal storage. And of course, you can install third party maps from sources such as on the card.

Another problem is that the battery life indicator seems to indicate low batteries when they aren't. I normally use lithium AA batteries because they have a longer life than alkalines, they work better in cold, and they are much lighter. In my previous Garmin units, an indication of less than 4 bars meant that the batteries were about done. The GPSMAP 66 drops to 3 or 2 bars within a hour or two of installing fresh batteries, yet the batteries test as good on a battery tester. This is minor and will probably be fixed in a firmware update.

Expedition mode should extend battery life to many days by letting the unit sleep much of the time, but it doesn't work on my 66s. Pressing the power but brings the unit to life but it never gets a satellite fix. I assume this means it's not recording track points while in Expedition mode. Again, this should be fixed in a firmware update.

And now for the positives- The big one is the vast improvement in the receiver over even the 64s, as noted above. I haven't used the unit in dense forest or narrow canyons yet, but under open sky, on the front seat of my car, or inside the house, it picks up the satellites and locks on more quickly. Part of this is perception- the GPSMAP 64 takes longer to go through the startup screens than the 66, but by the time the satellite status page comes up, the 64 has a satellite fix. In GPS/GLONASS mode, it typically picks up 8 or more GPS satellites and 3 or 4 GLONASS satellites, and the accuracy is usually 10 to 15 feet, sometimes better. The receiver also picks up EGNOS/WAAS satellites for differential correction to an accuracy of a few feet, but these systems are designed for airborne use and the unit doesn't usually pick up those signals except in an area with a clear, low horizon.

The unit can also use the ESA Galileo satellites when they come online in a year or so. Note that the satellite modes are GPS only, GPS and GLONASS, or GPS and Galileo. There's no way to use all three satellite systems at once.

The GPSMAP 66 series has WiFi, in addition to the Bluetooth of earlier models. This lets the unit check for and automatically download firmware updates whenever it's connected to the Internet through WiFi. You no longer have to use the Garmin Express app on a Windows or Mac computer. As a Linux user, I really appreciate that.

Another benefit of WiFi is that the 66 series downloads the GPS satellite ephemeris from the Internet, which means the next startup will be a warm start. Of course, this doesn't work in the field, but it may be worthwhile to turn the unit on at home, or another place with public WiFi, and let it run for a bit before heading out.

A word about accuracy- civilian GPS receivers, even the cheaper chips in smartphones, are as accurate as the most accurate maps published- the USGS 7.5-minute topographic series. This has basically been true since Selective Availability was turned off in 2000. The most important difference between GPS receivers is how many satellites they can receive simultaneously, which in turn affects how well the unit keeps it's position fix under partial sky conditions, such as deep forest or narrow canyons.

And finally, Garmin has now made their excellent BirdsEye satellite imagery available for free. You can download imagery for a defined radius around your present location, or pan to a different area on the map. And you can optionally store the imagery on a micro SD card- which is good, because high res imagery takes up a lot of space.

So I like the GPSMAP 66s. The fast satellite fixes alone are worth the upgrade from the 64s. And the advent of Galileo should improve that even further. Not that I'm of fan of touchscreen GPS's anyway, but even the latest Garmin Montana and Oregon units don't offer everything that the 66s has. Galileo reception is missing, strangely enough.