Comparing Alerts - speed, along the road/route, and TourGuide


There are several kinds of Alerts
1. Speed alerts
2. Along the road proximity alerts
3. TourGuide proximity alerts

In order to receive an alert,
1. your device must have alerts enabled.
2. you must have Custom POIs loaded (see note below)
3. your volume level must be sufficient (and not muted) to hear the alert

Note: certain newer Garmin Devices come with built-in School Zone Alerts. The school zones are not complete (we assume that Garmin will increase the zones as new maps are provided) and the alert can not be turned off.

Speed Alerts

If you are traveling over the "speed" set in an approaching Custom POI location, the device calculates a proximity distance at which to sound a speed alert. The proximity alert distance calculated by POI Loader is based on "speed" information in the file name or in individual POI names. This calculation uses the following formula:

Prompt Distance = 36 seconds * Speed.

This works out to the following distances based on the POI MPH speed value.
20 .2 miles or 1056 ft.
30 .3 miles or 1584 ft.
40 .4 miles or 2112 ft.
50 .5 miles or 2670 ft.
60 .6 miles or 3168 ft.

Note: it makes no difference as to the speed at which the device is traveling. The distance is dependent solely on the speed from the POI location. So, if you are going 60 MPH and are approaching a 20 MPH zone, you are going to have to use your brake to slow down

Along the road alerts

Let's assume for this discussion that you are on a perfectly straight road and are approaching a POI for which you want an alert. OK, I know that this rarely would be the case but the device can handle this for us, so just read on.

Visualize a rectangular box.
1. Your device is at the bottom center of the box.
2. The height of this box will be the proximity distance you have set - either by using the "manual" mode of POI Loader for a .csv file, or, by having a proximity distance imbedded in the POI coding of a .gpx file (which allow you to use "express" mode of POI Loader)
3. The width of this box is 196 feet
4. The road runs in the center of this box from bottom to top - so that the road has 98 feet of box on either side of it. Even though the road may make zigs and zags, your device internally straightens the road.
5. The POI location can be thought of as being on a line parallel to the top edge of the approaching box.

As you travel, the top of the box approaches the POI location. If the coordinates of the POI location are within the box at the proximity distance along the road, the alert will be triggered.

However, if the coordinates of the POI location are not within the box - that is, the POI location is more than 98 feet from the center of the road - you will not get an alert.

By way of explanation, Garmin's native unit of measurement is the metric system and 30 meters is the alert side to side requirement. Inside 30 meters, an alert will sound. Outside 30 meters and the alert will not sound. 30 meters is equivalent to 98 feet.

It is for this reason that Mahoney goes to great pains in making sure that the coordinates of rest areas in his Combined Rest Areas file ( are positioned somewhere on the exit ramp to the rest area - NOT at the building with the rest rooms way back off the road somewhere.

Just to muddy the waters a bit concerning Rest Areas, you may, from time to time, get an alert for a Rest Area that you cannot turn into from the side of the interstate or divided highway along which you are traveling. Why? Well, the coordinates of this Rest Area which is actually on the other of this divided highway ARE within the top of the rectangle BUT you can't get there. Whenever you encounter one of these Rest Areas, make a note of it and contact Mahoney.

Along the Route alerts
Using the same "rectangle" as discussed above, understand that, if you are traveling a "route", your device considers that you are on a single road and straightens it to be the centerline of the rectangle.

To illustrate, I am including below a post that was written by Hornby in 2007.

Hornby wrote:

In this example, imagine you are travelling up the screen on Road A. You could turn right onto Road B and pass a School after 0.5 Mile.
Say Point {X} is 1 mile from the intersections of Road A and Road B (not easy this!)


+-Road B--0.5 mile to [SCHOOL]---->|
X <-Point X

[Along the road] (just driving with GPS on)
If you set a Proximity Alert for the school at 1.5 miles, the alert will sound when you turn right onto Road B (i.e at 0.5 miles).
If you continue driving up Road A you will probably not get an alert at all.

[Along the route]
If your Route involves making a right turn onto Road B, then the alert will sound at 'Point X' - 1.5 miles from the school, by road.

TourGuide alerts

Visualize a circle.

At the center of the circle are the coordinates of the POI location. The radius of this circle is the proximity distance you have set - either by using the "manual" mode of POI Loader for a .csv file, or, by having a proximity distance imbedded in the POI coding of a .gpx file (which allow you to use "express" mode of POI Loader).

Whenever your device enter this circle, you will get an alert. This can lead to some interesting situations because you should never assume that you can easily navigate to the POI. You might be just across a river from a POI and the nearest bridges are miles in either direction.

The major distinction between "along the road" or "along the route" alerts and "TourGuide" alerts is that the "general rule" from POI Loader Help is that the word "TourGuide" (without the quotes) must be a part of the POI file name AND there must be a sound file (.wav or .mp3) with the exact same name as the POI file (.csv or .gpx) to the left of the extensions.

TourGuide may occur anywhere in the file names - but the spelling must be exactly as shown - with a capital "T" and a capital "G".

HOWEVER, one of our members determined that having a "Folder" whose name included "TourGuide" would result in all POI files within that folder being treated as "TourGuide" files without the necessity of each individual .csv, .gpx, .mp3 (for those devices with a mp3 reader), .wav, and/or .bmp file needing to have "TourGuide" in the individual file name. This was subsequently verified by alandb and me.

Since this was a shock to many of us, charlesd45 did some research and found that POI Loader Help made this statement:


You can also associate .bmp images with all the data files in a subcategory. For example, a customized bitmap called "restaurants.bmp" would be associated with all the points in a "Restaurants" subcategory. Custom bitmaps associated with individual file names take precedence over custom bitmaps associated with subcategories.

. As charlie commented, it made since that a subcategory of "TourGuide" would behave the same way

Change History

  • jgermann - Nov 7, 2016
    11/07/2016 Corrections

  • jgermann - Nov 18, 2015
    11/18/2015 added more explanation

  • jgermann - Nov 14, 2015
    11/14/2015 Added info on TourGuide as a "Folder" or Subcategory