FAQs

How much technical expertise is required to make the maps?

Going from your GPS system to Google Earth is pretty simple. Follow instructions that came with your GPS system to write out a .gpx file. Newer systems probably can do this directly. If not, there are conversion programs on the web that can make the .gpx file from whatever your GPS system writes out. Google Earth can read the .gpx file. After that, you will use Google Earth to manage the tracks and move them within folders, etc.

How long does it take to make the maps?

I did the Chelmsford Lime Quarry Conservation Area in about 3 hours - 2 walking with the GPS and 1 on the computer. It took longer in the beginning because of the learning curve.

How do you share the maps?

In Google Earth, right click on the main folder where your maps are and pull down "Save as...". Specify a file name and write out a .kmz file. You can email the .kmz file to others who have Google Earth (they save it locally, then load it using file->load). Or you can share it as I have on the Carlisle or Chelmsford web page, by posting the file on your web site and giving people the URL.

People can only see the file in Google Maps if you have put it onto a web site. You can type its full URL (for example,
http://www.minitreks.info/maps/carlisle_trails_gmaps.kmz)
into the "Search Maps" space at maps.google.com. Once you have brought up the map this way, click on "link this page" to get a text link you can paste into an email, or a small map link you can paste onto a web page.

Why do I see an error message in Google Maps?

Sometimes you see the message "Parts of http://www.minitreks.info/m... could not be displayed because it contains errors." when you load a map into Google Maps. You can click on the "Show errors" link to get a line number. I have seen two causes:

1. Google Earth seems to be using something in its .kmz file <style> tag that Google Maps can't digest. This happens on nearly every map I have made.

2. Google Earth uses a negative number for altitude. I have seen this on both a path and a placemark. I believe it happened when I copied the path or placemark within Google Earth during construction of the map. I fixed it in Google Earth by bringing up properties on the offending element, clicking on the altitude tab, and fiddling with the altitude slider, leaving it at 0 or 1, then resaving the file. In the case of the path, the altitude was already at 0; resetting it was the key.

To narrow down your problem, save the map as a .kml file and edit it with a text editor so you can look at the offending line. You should be able to tell if it is a placemark or a path by the content of lines just above and below. Alternatively, you can use the validator at feedvalidator.org, which will both tell you what the error is (if any), and show you the file with line numbers.

Files with the "<Style> contains syntax errors" message usually pass the validator OK, so I assume the problem is with Google Maps.

Where did you get your trail names?

I made most of them up with impunity. If there are trail names on any of the paper maps I find on the web or from Town Hall, I use those. Otherwise, I make up good, practical, boring Yankee names, because I need something to call them. I'm always hoping for input from trail committees.

On your map, there is a private or discontinued trail.

Probably I didn't know it was private or discontinued. Probably other trail users don't either. Unless there is a sign, if you just leave private trails off the map, the walker doesn't know whether it private or is just missing from the map. One way to deal with these is to show the trail as a short stub and mark it with a No Entry icon, with or without a "private" label:

Let me know about any you want me to change on my site.

How frequently should one take track points on the GPS receiver?

Every 5 seconds works for me. That captures the winding nature of these small community park trails pretty well. On the computer, I edit out many of the track points on the straight sections of the trails to reduce the file size and, hopefully, loading time.

What about waypoints, or 'marks'?

I press "mark" on my GPS receiver to record points of interest, like the quarries in Lime Quarry, and parking lots, and the like. My GPS software calls them "Waypoints". These translate into "Placemarks" in Google. You can give them a description which can contain html formatting, photos, links to web sites, etc., and you can pick an icon for them (theoretically you can create your own icon, but it might not fare well on Google Maps). In Google Earth, you can change the size and color of both icon and label. Historic markers make great waypoints, because you can add the historic context.

Placemarks keep a set size as you zoom in on the map. So when you are looking at the whole town, the placemarks look huge and dominate the screen. As you zoom in, they look smaller because everything else gets bigger, and they become more useful.

Each placemark takes real time to load, so in Google Maps, be frugal. I have been leaving out boardwalks and bridges and so forth, because as important as they are to the pleasure and convenience of the trail, they aren't important for planning today's walk. In Great Brook State Park, there are so many small interconnecting trails that they have added numbered intersection posts. I put small placemarks in for these in the Google Earth version because they are very helpful finding your way around the park. But in Google Maps they come up full size and eat up load time, so I left them out.

Is there a risk that posting the trails this way will bring unwanted trail traffic?

Yes, I think it could. Most towns have some trail maps online, but these will be more accessible, and may eventually link up with other towns. Your trail stewards, trail committee, or whoever is interested or responsible should discuss it. If some official body from the town asks me not to post the town trails, I won't.

Is there a particular technique for editing the paths?

Because Google Earth's path editing tools are primitive and a little buggy, you will be much less frustrated if you edit the paths as much as you can in your GPS software before importing them to Google Earth. It's OK to move the paths a little - at best your GPS receiver might be 10 to 15 feet off anyway. The maps that you get with your GPS device aren't very accurate - not nearly as accurate as the satellite image on Google, so don't use map features to nudge trails until you transfer to Google. On your GPS software:

1. Make sure that intersecting trails share a common point.

2. Delete all the points you can in straight trail sections. You should be able to delete 1/2 or 2/3 of the points you have unless the trail is really winding.

3. Name the trails. Split up any track that moves from one named trail to another.

4. Join up tracks that make up one named trail.

Once you have imported the trails to Google Earth, you can nudge them into place on the satellite image in open areas where you can actually see the trail. You can also nudge the endpoints to meet roads and parking lots exactly, assuming that you don't hit any path editing bugs.

If you are having trouble editing paths in Google Earth (can't select a point without closing the path into a polygon) try these hints:

1. Edit the "virgin" path, as it was created from the .gpx file, before changing its altitude.
   

2. When you click on an endpoint to select the point, if the path starts to close into a polygon, hold down the button, then drag the endpoint away from the rest of the path.
   

3. Zoom well in on the path, so that its points are not piled up one on another.

In your Earth maps, what are the greenish blue wide tracks for?

The user's problem in these interactive maps is matching a trail name and length on the left panel with the actual trail on the right. In Google Maps, you use the trail colors. The problem, of course, is that some people are color blind, and even the rest of us have trouble telling orangey red from red. The other technique in Google Maps is to turn a trail on and off using its checkbox while watching the right hand screen to see it blink. It works OK, but it's a little primitive.

In the Earth examples, I have put ALL the trails down in one subtle color (greenish blue). They are in their own folder, call "All trails". Then, in another folder called "Trail lengths", there is another copy of each trail in a bright color, arranged so you can only turn on one at a time. As you wander down the radio boxes on the left hand side, you see the corresponding trails light up, one at a time on the right. I think this is easier to see than the color method. Meanwhile the "All trails" copy stays steady to give you overall context.

When I make the Trail lengths brightly colored trails, I set their altitude to be 1 meter above the ground. This makes sure they are not obscured by the All trails copy.

In your Earth maps, there are trails made up of segments of other trails. How do you do that?

My pet name for these is "meta trails". For example, in Google Earth, open "Trail lengths" under "Cranberry Bog". The "Hike Thru" trail there is a meta trail. It is really a folder containing pieces of other trails.

When I am editing the trails in the GPS software, I decide what will be the main trails and what meta trails I want to make from them. I make the long regular trail; for example, "Upper Loop". Then I copy it, break it up into trail segments called, for example, "Upper Loop A" and "Upper Loop B", and paste the main "Upper Loop" trail back in. Now I have two copies of the trail, one is broken up, the other is whole.

After importing those trails into Google Earth, I put all the trail segments into "All trails", and the long trail into "Trail lengths". Whenever I want to use a trail segment (like "Upper Loop B") to make a meta trail, I copy it from "All trails" and paste it into the meta trail folder. Then I change the color, width and transparency to match the characteristics of the parent trail (in this case, peach for Upper Loop).

Normally, I tell Google Earth not to allow trail folders to be opened. This reduces the complexity. I have left the folders for the Hike Thru trail open in the demo so you can see what I'm talking about.

Can I extract the tracks back out of Google Earth?

Yes, but it will probably require a file conversion or two. You write out the .kml file, then use a file converter to make a .gpx file. I haven't found a converter that preserves the track names yet.

Can I add photos?

Yes. You can put html tags into a path, folder, or waypoint description. Post a .jpg onto your web site and embed it into the description with an <img> tag. For example,
<img width=300 src="http://www.minitreks.info/images/cranberry_harvest.jpg" alt="Cranberry harvest 10/15/2007">
See the Carlisle Cranberry Bog for an example of the output. Photos will show up both on Google Earth and Maps, as long as the web site where they are posted is online.

Why are there more folders in the Google Earth example than the Google Maps example?

Google Earth stores the state of a folder when you save the file. So if a folder is closed or deselected when you write the file, it will be that way initially when users view the file. Google Maps always brings each folder up open and selected, making it too slow and cluttered. I format the Earth version first, then make a copy and delete lots of stuff for Maps.

What file types are involved, and how can I convert?

The most important GPS file type is the .gpx file type. This is an XML-type file that is very "shareable". That is, you can post it on the web for other people to use on their GPS device, you can load it directly into Google Earth, etc. I think .gpx stands for "GPS Exchange". Garmin MapSource software can write this sort of file if you ask it to.

Google Earth can write out two file types: .kml and .kmz. KML stands for "Keyhole Markup Language". KMZ is a compressed ("zipped") version of the same. If you want to convert a .kmz file to a .kml file without Google Earth, you can simply "unzip" it. On windows, change its extension to .zip and then you extract and open the .kml using the normal File Explorer.

Google Earth can load .gpx files, but cannot save them.

I didn't do all that much research into converters. I did one brief internet search which turned up a few which solved my immediate problem. Eventually I'll go back and try to put together a more coherent list. It seems to be a rapidly evolving field. All these files are XML-type files, and can be converted with XSLT technology.

www.dnr.state.mn.us can convert from .kml to .gpx. This closes the editing loop, allowing you to export half-edited trails from Google Earth back to MapSource where you can use the track split and join tools that Google doesn't have. And you can also get them back into your GPS receiver to take with you on your next tracking expedition. Unfortunately, I cannot read the resulting .gpx file with my Garmin MapSource software. I have to first run it through another free application, GPS Trackmaker. It reads the .gpx file, then writes it back out, then I can read it from other applications.

Keyhole has some XSLT conversion technology (I haven't played with it much yet). www.gpsies.com can do lots of file conversions, too.

How were the Chelmsford Parcel Overlays done?

Exact parcel boundaries (the "lot lines" established by surveyors and registered with the town) are extremely helpful in establishing accurate boundaries to make an overview map of the conservation areas. I found Chelmsford's parcel boundaries at gis.townofchelmsford.us. It would be best to get direct access to the GIS system for the town, and write out the GIS system's shapefiles for the parcels -- maybe someday I'll pull that off. But for starters I used the GIS server on that website to zoom in on rectangles containing one or more conservation areas, turned on relevant GIS overlays like conservation and protected areas and town property, and took a screen shot (alt-print screen on Windows). Then I pasted the screen shot into a photo editor and saved it as a .jpg file.

The deeper the zoom, the more accurate the overlay. But it's important to capture roads on all sides of the target area, to place the overlay accurately. (You can see where the parcels all line up along the roads even if roads aren't turned on in the GIS image).

I overlayed the screen shot onto the Google Earth map in the right place (right click on the map folder, pull down add->image overlay and browse for the screenshot image.) Then I stretched it very carefully until all roads on all sides line up. It's surprising how well the image can match up with the map, as long as you only use roads for alignment (because they show up on the satellite image).

When you save a .kmz file with overlayed images, the .zip folder contains the images themselves - you don't have to upload them onto a web site first.

How do you make the overview maps?

Start with a parcel overlay of some sort, as described above. For Carlisle I didn't have exact GIS input, but I did have an overall map put out by the town showing roads and conservation area boundaries (right), so I used that.

1. In Google Earth, perform the overlay.

2. With the overlay on, zoom in on one conservation area. Create a polygon for it (right click on the map folder, choose add->polygon). While the properties dialog for the polygon is up, click on one corner of the conservation area, then another, right around, tracing the area. Set the polygon to the desired color, and about 50% opacity. Name it after the conservation area.

3. In the properties dialog, under the description tag, add an HTML pointer for a detailed map of that area (for example <a href="xxx">Detailed map</a>).

4. Bring up your detailed map in Google Maps as described under "how to share the maps" at the top of this page. Click on "link to this page", and copy the "email" version of the URL for the map.

5. Back in Google Earth, in your properties dialog, paste the map URL over the "xxx" in the example. Now when you bring your overview map up in Google Maps you will see the polygon. If you click on the polygon you will be presented with the link to the detailed map.

You can get more accurate results if you do this in several steps, using one small section of the overlay at a time, rather than trying to overlay the whole town at once.

We have trail overlays on our town GIS (Geographic Information System) maps. Can we use those?

Yes, you can at least get the tracks. I haven't yet figured out how to import the trail names. You can convert a shape file from ArcView into .gpx, and from there to .kmz. www.dnr.state.mn.us has an application I've been using. It reads shapefiles. You first have to calibrate the map by looking in the .prj file that ArcView writes out. Launch DNR Garmin, Pull down "Set Projection". Load the .prj file in that dialog, and choose the right datum (you can find this in the .prj file, which you can edit with a text editor) in the Datums/Projections menu. THEN load your shapefile. Write out a .gpx or .kmz file, load it into Google Earth, and Voila! If you get the wrong datum, you get a nice set of trails, but they end up in the ocean somewhere.