How To Make A Trail Map Using Google Earth

Making The Map

Examples of four separate GPS track logs displayed on Google Earth imagery. Note the map scale, and note that the track logs rarely overlap exactly. The two waypoints in the left-hand picture are both at the same trail intersection.

The left-hand picture shows a relatively neat set of track logs; note the map scale and the relatively tight spread. The right-hand picture shows a relatively sloppy set of track logs.

This is a fairly typical set of track logs.  

Here's a breakdown of the tasks:

Planning The Map

It helps to do some planning before you start making the map, especially if the map is going to contain a lot of information. Some things to think about:

Creating And Editing Paths

Before I continue with more tips and notes about making the map, I want to explain how to create and edit paths, since it's not covered very well in the Google Earth help system.

You create a path inside a folder by right-clicking the folder in the "Places" sidebar, then selecting "Add" and "Path". A dialog box opens and the cursor changes to a box with crosshairs. If you want a particular color and line width, click the "Style, Color" tab in the dialog box and modify the settings. When you create additional paths, it remembers the style and color settings until you change them or edit a path with different settings.

Now you start left-clicking the mouse to create a series of points which become connected with straight lines. When you're happy with the initial path (it can be edited later), click "OK" in the dialog box. The dialog box closes and the cursor changes back to a hand.

To edit a path, right-click the path in the "Places" sidebar, select "Properties", then the dialog box opens and the cursor changes to the box with crosshairs.

This is what a path looks like after it has been created (color = white, line width = 4). The points were drawn from left to right, although you can't tell by looking at the path. The order is important for inserting new points in the path (see below).

This is what the path looks like when you open the properties dialog box to edit the path (the dialog box is not visible in this picture). All the points that make up the path light up and the cursor changes to a box with crosshairs. If the cursor is not on any point, the points are all red.

If you hover the cursor over a point (but don't click), the point turns green and the cursor turns into a hand.

At this time you can hold the left mouse button down and drag the point to a new location. Notice the point is now blue.

Once you click or drag a point, it is selected and turns blue, even if you move the cursor off the point.

To insert a new point, you must know which direction the points were originally drawn (in this case, left to right). That's because you can only insert a point after a selected (blue) point. Knowing this was left to right, click the mouse and Google Earth inserts a new point after the blue point. The new point is initially green, but turns blue (selected) once you move the cursor off it. You can keep clicking to create more new points after the blue point (which is how you extend a path, if you select the last point). To delete a point, left-click the point to select it, then right-click it to delete it. You can only delete a point if it is selected (blue). (In the picture, assume that I delete the point I just added before I go to the next picture.)

Supposing you don't remember which way the points were originally drawn and you click on the "wrong" side of the point to insert a point to the left of the blue point. Google Earth always remembers which way the points were drawn, and it still inserts the point to the right (in this case), distorting the path to accommodate the new point. The path now consists of the first three red points (left-to-right), then the path goes the "wrong" way to the green point, then the last two red points.

Since this isn't what you want, immediately right-click the new point to delete it. Then you have to click point #2 (left to right) to select it, then click where you wanted the new point, and it will appear in the proper place.

By the way, be sure to save your work frequently while you're creating and editing paths. Some versions of Google Earth have a tendency to crash, which instantly wipes out all unsaved changes. Also, before you start making major changes or additions, it might be a good idea to create a backup by saving the top-level trail folder under a different file name. When saving data, keep in mind that Google Earth stores the data for "My Places" in its own private folder on your hard drive, which is not part of the "My Documents" folder hierarchy. If you're saving important information in "My Places", make sure the information gets backed up somewhere else, too.

Drawing The Trail Paths

If you've accumulated multiple track logs and lots of pictures, you ought to have enough information to accurately draw the sequence of right/left twists and turns for a trail. Don't be fooled by an "obvious" route in the imagery—the trail may not follow clear areas and may turn this way and that way for reasons that are not apparent by looking at the imagery. Trust your track logs and photographs.

Rough-in the trail by creating a path, then clicking along the general flow of the track log lines. Don't try to get it perfect right away, since later on you can tweak it turn by turn by referring to your photos.

Occasionally the trail might be slightly visible in the imagery, and you can blink the track log lines on and off to help you fine-tune the trail path. Do this by hovering the mouse over the "check box" for all the track logs in the "Places" sidebar, then clicking the mouse repeatedly while staring at the imagery. As you repeatedly check/uncheck the track log check box, the track log lines repeatedly appear/disappear on the screen. You might discover that the trail is faintly visible (see below).

You can simulate blinking the track log lines on and off by moving your mouse back and forth over these two choices (you don't have to click the mouse):  Track Logs On  Track Logs Off.  If you look carefully, you can just make out portions of the trail. You must enable scripts in your browser to make this work.  

Supposing you don't have any trail photographs and you can't see the trail in the imagery. You'll have to draw the path by "visually averaging" the track log lines. You'll notice that the track log lines rarely overlap completely, but you should be able to make out some correlation between the lines. Pay particular attention to the directions that the lines move as well as the exact positions of turns. In many cases, even though the track logs don't exactly overlap, the directions of the lines are very similar, running more-or-less parallel. Therefore the path you draw should be parallel to the track log lines. In other words, the track log captures not only position information, but also direction information. Although the position might not be exactly repeatable each time you walk the trail, the direction might turn out to be fairly accurate each time. This is more information that you can use to draw a more accurate path.

As an aside, you can measure how long the trails are in the real world by using the "Ruler" tool in Google Earth.

Placing The Placemarks

If you're creating placemarks for points of interest, you can have Google Earth display a picture of the point of interest when you click the placemark. Just include an <img> HTML statement in the placemark verbiage. To make the picture display quickly, keep the size relatively small (for example, most of mine are 420 x 315 pixels) and use some JPEG compression to reduce the file size (40 to 50 kilobytes). You need to upload all the pictures to an internet web server that you can access, but choose the location carefully. Every placemark will have a hard-coded absolute URL to its picture, and you don't want to have to edit dozens of placemarks if the web location changes.

It's also useful to make a special placemark that includes a map legend, plus any other general information about the map (like who made it!). For my map, I made a custom icon that was very big and obvious, which when clicked would display a jpg image containing the legend.

When you think you're all done making your trail map, make a final pass through the folders in the "Places" sidebar to make sure all the styles/colors are consistent. Then test every single map feature to make sure everything works. Finally, you have to upload the main kmz file to an internet web server to make it available to people browsing the web. You might have to configure the "mime types" on your web server so the server provides the correct "file type" information to a web browser (that is, to make sure the server tells the browser that a kmz or kml file is processed by the Google Earth application).

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- John Santic

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