How To Make A Trail Map Using Google Earth

Capturing The Raw Data

An example of very detailed imagery from Google Earth showing a trail bridge and individual trees in Quiet Waters Park, Annapolis, Maryland.   This imagery showing a stream channel at Calvert Cliffs State Park is much less detailed. Note the scale—this picture shows much more territory than the other picture. If I zoomed-in this picture to the same scale as the other picture, it would be a totally useless blur.

This step will be easier if you break it up into a few tasks:

Plan Your Fieldwork

Before you get started on your trail map project, check out the imagery on Google Earth to make sure it's detailed enough for your purposes. Some regions have very detailed imagery where you can see individual trees and even people, but other areas show much less detail (see the pictures at the top of the page).

You have to decide how detailed and accurate you want your trail map to be. For example, if the imagery is very detailed (where you can see individual trees), you can make your map very detailed by trying to accurately locate trails and points of interest to within 10 feet or less. On the other hand, if the imagery is not very detailed, there's not much point in trying to make your map very detailed and accurate. At a usable scale, any fine details of the trails would be invisible, and nearby points of interest might be right on top of each other.

This has a big effect on how you capture the raw data. For example, if the imagery is very coarse, there's not much point in drawing a very detailed and accurate trail map. In this case, you might be able to walk the trail only once, while capturing a single GPS track log and taking occasional photos of major points of interest. But if the imagery is very detailed and you want an accurate and detailed trail map, you will have to walk the trail several times to capture multiple track logs and waypoints. One time you walk the trail, you'll also take lots of photos of the trail and points of interest.

The reason you need multiple track logs is that typical GPS accuracy while walking in the woods is 15 to 25 feet, and frequently worse. If you want your map accuracy to be better than 10 feet, you need multiple track logs that you can "visually average" while drawing the trail in Google Earth. To make my Quiet Waters Park trail map, I walked each trail four times. This is not as bad as it sounds, since I walked a trail out and back on one day, which counts as two times, then out and back on another day, which counts as another two times. I usually captured waypoints of trail intersections and points of interest while walking out on the first day and again while walking out on the second day, for two complete sets of waypoints. Every time I captured a waypoint, I made a voice note, plus on one of the times I walked the trail, I took a full set of photographs of trail details and points of interest.

You might think it's overkill to capture so much information about the trails (multiple track logs, waypoints, photographs), but once you get back to your computer and start drawing the trail on Google Earth, you'll be glad to have all that information. You can rarely see an unpaved trail in the Google Earth imagery, since the trail is usually narrow, low-contrast with respect to its surroundings, and frequently hidden by trees. Also the trail rarely follows the route that would seem obvious in the imagery, so you really have to depend on the data you've captured. Since the track logs and waypoints rarely overlap exactly, you really need several copies of multiple types of information to draw an accurate trail map.

Based on all the planning that you've done, make up a master to-do list on your computer of all the tasks that need to be done. For example, you might split up a park into different sections and walk the trails on different days. Keep track of how many times you've walked each trail, and whether you have a full set of photographs for that section of the park. The to-do list also keeps track of the work to be done on Google Earth (drawing paths, adding placemarks, etc.). If your trail map project is a part-time effort that takes a long time to complete, you need to keep a list to remember what you've done and what you still have to do.

When to go hiking - I do most of my trail hiking in the off season (late fall through early spring), to avoid mosquitos, flies, chiggers, ticks, and poison ivy, plus it's cooler for more comfortable hiking. Some of the trails are not heavily used, and they can quickly get overgrown by grass and weeds during the growing season. Personally, I also like the cold gray days in winter when it seems like I have the park to myself. If the ground is frozen, I can walk across the boggy areas without getting my feet wet, which is an extra bonus.

Prepare Your Equipment

The night before a hiking day, prepare your equipment. Recharge the NiMH batteries just before using them, rather than after using them, since they lose charge rapidly. Make sure your camera is charged and the memory chip is empty. Likewise, if you use a voice recorder, make sure the batteries are good and the memory is empty. Clear out all the old trail map waypoints from your GPS, because you don't want these old waypoints to become duplicated on Google Earth every time you download a new batch of track logs and waypoints.

With the Garmin GPS, there's an easy way to clear out all your old trail map waypoints while preserving other waypoints that you still need: When you capture your first waypoint on hiking day, before saving the waypoint, select a different waypoint symbol, one you won't use for anything else. When you save subsequent waypoints, the GPS will keep using this symbol. Then on your next hiking day, you have to clear out all these old waypoints. On my GPS, I can tell it to delete all waypoints that use a certain symbol (the trail map symbol), so I don't have to delete each waypoint individually. Waypoints that use other symbols are not affected.

If you're very finicky about details, you can also check the date/time of all your electronic gadgets. The time displayed by the GPS is very accurate, so you can check your camera and voice recorder to make sure their time is close to the GPS time. This makes it easier later on to correlate pictures and voice notes with where you were on the trail, since each point in the track log includes a very accurate date/time.

Check your master to-do list and make up a working list of all the detailed tasks you hope to complete on hiking day.


As soon as you arrive at your working location, turn on your GPS and put it someplace with a good view of the sky, so it acquires all the satellites and minimizes the estimated position error. Sometimes the satellite geometry might not be so good (not many satellites visible and/or satellites close together) which can degrade the accuracy. If you plan to walk the trail twice (out and back), by the time you're walking back, it's likely the satellite geometry will have improved, so it's no real cause for concern.

There are a bunch of settings you should check on your GPS:

Once you reach the trailhead, enable track logging and start walking. If you stop to take a picture or capture a waypoint, temporarily disable track logging. You should also temporarily disable track logging if you need to walk off the main trail to investigate a possible side trail or to check out something interesting. The goal is to have track logging enabled only when you are actively walking on a trail that you want to include on your Google Earth trail map.

This avoids wasting track log memory when you're not walking, and avoids producing a confusing track log display in Google Earth. If track logging remains enabled while you're standing still, the usual small position errors cause your position to dither a few feet, and perhaps up to 10+ feet. Once you upload this to Google Earth, the track log will look like you were walking all around a small area, when in fact you were standing still. If you keep logging when you wander off the trail, you'll just clutter up the Google Earth display with lots of spurious tracks, and days or weeks later, you won't even remember what it all means. Remember to re-enable track logging when you resume walking.

To help you accurately locate trail intersections and points of interest, stop walking, disable track logging, and capture a waypoint. To improve the accuracy of the waypoint, use "averaging mode" if your GPS supports this feature (I average for 30 seconds or so). Let the GPS autonumber the waypoints, and don't bother filling in the comments field for the waypoint. Instead, record a voice note of the waypoint number and its purpose, because it might not be so obvious just looking at the raw data on Google Earth. Remember to re-enable track logging when you resume walking.

If I'm trying to make a detailed and accurate trail map, I take lots of pictures of the trail context, especially trying to capture the sequence of right/left twists and turns. As I approach a turn, I take a wide-angle picture of the area around the turn, so you can see which way the trail is currently heading and which way it turns. During the turn itself, I take a wide-angle picture capturing some of the same trees that were in the last picture, to establish continuity of context. Once I'm headed in the new direction, I take a picture straight down the trail, which usually shows the next turn in the distance. Then the picture-taking process repeats at the next turn.

You should follow a systematic plan for capturing all the trail information. For example, if there are lots of confusing side trails, always walk to the right when the trail branches, until you reach the end of the side trail. Then backtrack and take the next side trail, always taking the right branch. Eventually this strategy will cover the entire main trail and all the side trails on both sides of the main trail. This assumes you walk out and back on the same day (a round trip), which lets you capture side trails on both sides of the main trail, following the "keep right" strategy.

You might be trying to make a very detailed trail map that documents all trails, major and minor, but if you're walking through a wooded area that is deer habitat, you need to recognize deer trails so you don't bother walking them or logging them. Also, a human trail may eventually turn into a deer trail, at which point it should be abandoned. A deer trail is usually narrow (six to twelve inches), may have low headroom (for people), and may wander or deliberately go into an area of dense brush and not come out. Human trails are usually wider (one to two feet), are more direct and deliberate, have full headroom, and avoid areas of dense brush if possible.

Examples of trail photographs that maintain the continuity of the trail context. In general, the background of one picture becomes the foreground of the next picture, with enough overlapping detail so you can see exactly how the trail progresses.


Process/Preserve Data

Download all the raw data to your computer:

Organize your data effectively, such as storing all the information from one trail hiking session in a single folder whose name includes the date of the hiking session. If you use the date in a folder or file name, specify it as "year-month-day" so once you accumulate multiple folders/files, they will automatically be listed in chronological order in the file browser (which sorts names alphanumerically).

To download track logs and waypoints, I have some special instructions for the Garmin GPSMAP 60Cx since it is capable of storing very large track logs in the external memory chip. For smaller track logs that fit in the main track log memory, or for other GPS models, skip ahead to where I explain downloading into Google Earth Plus.

If you've been hiking and logging track points for longer than 2 hours 46 minutes (at one track point per second), the main track log memory has filled up and wrapped around, overwriting old data. This means the main track log memory does not contain the complete track log of your hike, and in fact, should be ignored. Instead you need to retrieve the track log from the external memory chip, which is a little complicated:

Connect the GPS to your computer using the USB cable, but do not try to download the track log with either Google Earth or Garmin MapSource. Both of these programs only access the main track log memory and not the external memory chip. Instead, on the GPS, go to the Main Menu and select "Setup", then select "Interface". At the bottom of this screen, you should see a button called "USB Mass Storage" which you should select. This installs the GPS external memory chip on your PC as a simulated external disk drive. Note that the GPS user interface (buttons and display) can not be used while the external memory chip is installed as a disk drive. On your computer, run Windows Explorer and open My Computer. You should see a new disk drive which is the GPS external memory chip. Select this disk and find the gpx file with the correct date (when you went hiking) and "drag and drop" the file to your hard disk. Then in Google Earth, use the File->Open menu command, specify "Files of type: Gps", and open the gpx file on your hard disk. From this point forward, it works like downloading from the GPS, as far as operating the controls and saving the data in Google Earth.

When you're done downloading the gpx file from the GPS external memory chip, you need to uninstall the GPS external memory chip from your computer. In the computer's System Tray, click on the icon that says "Safely Remove Hardware" then click on the USB mass storage device that is the GPS. Once the external memory chip is uninstalled, the GPS user interface starts working again. Go back to the track configuration screen, select "Setup", select "Data Card Setup", then delete the gpx file that you just downloaded. Don't let track log files accumulate here, because over time they will fill up all the extra space in the external memory chip.

To download GPS track logs and waypoints into Google Earth the normal way, connect the GPS to your computer using the USB cable. Run Google Earth Plus, then select Tools->GPS, check "Waypoints" and "Tracks", uncheck "Routes", check "Draw lines..." and "Adjust altitudes...", uncheck "Create clickable...". The reason you "Adjust altitudes to ground height" is that the GPS elevation data will practically never agree with the Google Earth elevation data. This can leave the track log line floating in space above the ground or even disappearing into the earth. By adjusting the altitudes, the track log line will always be at ground level, as far as Google Earth is concerned. And the purpose of this whole project is to draw the trail map on Google Earth, which will use the Google Earth elevation data anyway.

Finally, click Import and wait while the data is downloaded from the GPS.

If you can't see all your GPS data on the screen, try turning off the Google Earth Timeline feature (View->Show Time->Never). If Timeline is active, your data is filtered by the time setting, and you have to futz with the timeline to make all the data visible.

Now you have to clean up some of the data in Google Earth. For the Garmin GPS, there is usually an extra bogus track log called "ACTIVE LOG" that I delete. Then I open the Waypoints folder and delete any waypoints not associated with the trail map (like some favorite waypoints that I leave in my GPS), plus delete any waypoints that are accidental exact duplicates of waypoints already downloaded. In Google Earth, you can't select multiple waypoints to delete, but you can click the first waypoint then keep alternately pressing Delete, Enter, Delete, Enter, etc. on the keyboard.

The most important thing is to remember to save the GPS information you just downloaded. You can keep a special kmz file on your computer that contains all the GPS information for this trail map. Open this file, which places it in Temporary Places, then drag the folder containing the GPS information you just downloaded and drop it into the kmz file folder. Finally, right-click the kmz file and select "Save Place As" to write the information back out to your hard disk. When you exit Google Earth, don't bother keeping anything that was in Temporary Places, since you already saved it.

Download all your pictures and voice notes. Like I mentioned before, I manually transcribe all the voice notes into a text file, the file name of which contains the date in a format like I also mentioned.

Update your master to-do list, checking off things you've done and adding any new items you came up with. You can also keep track of your progress by marking up the Google Earth display with special paths and/or placemarks. These items are just for your information and are not part of the official map, so they should be stored in a separate folder.

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