Living with a Garmin: The Circular Routes Problem
Circular routes confuse the GPS. (By 'circular' I mean any route that eventually returns to its starting point. By contrast a 'linear' route would be one that goes from point A to point B.)
As you set off, the GPS detects that the 'destination', ie the final point in the Route, is nearby, and decides to take a shortcut to that point. Often, this is not at all obvious on screen (no error messages etc) and the first sign that something is amiss is that the GPS appears to be counting backwards, or pointing you back towards the start. This is often interpreted as some sort of fault. (At this point, more often than not you can simply fix the problem by reloading the Route and so forcing a complete recalculation.)
Of course, you loaded a Route with lots of intermediate points that had to be visited, so why does this confusion happen and how can it be prevented?
The problem arises because a route is, by definition - according to my Oxford dictionary - "a way or course taken from one place to another".
A cycle ride, on the other hand, more often than not finishes at the same place it started (home, or a car park, campsite or hotel, or event HQ).
It starts to become more obvious why there might be a problem.
And while we're looking at definitions, here's another one, this time of a 'Route' with a capital R - that is a Route in the sense of a GPS programmable file - "a collection of points (latitude and longitude) listed in the order in which they are to be visited".
(That's my own definition, by the way - Wikipedia simply says "a series of two or more waypoints".)
That last is what we expect our Garmin to do - follow a route visiting each intermediate point along the way. Very much like following a Routesheet on a cycling event. However, with most Garmin GPS models and certainly all those that I have used (Geko, Etrex, Dakota), if the GPS detects a significant shortcut whilst following a Route, it will go into 'helpful mode' and quietly adjust the Route in its memory, to use that shortcut.
This applies equally in Follow Road, Off Road and GPXX modes.
The rule appears to go something like this - again, this is just my interpretation -
"While navigating a Route, the 'next' intermediate point should always be closer than any subsequent point."
When this rule is broken, there is a potential shortcut situation (though it works slightly differently depending on whether you are navigating in Follow Road or Off Road) and a good chance that the GPS will reorganise the Route to make use of that shortcut. The classic 'circular route' problem is just the extreme special case of this rule being broken. But it can kick in in all sorts of other common cycling situations, such as figure-of-eight routes, or routes with a section of out-and-back somewhere within them, or even just an acute dog-leg.
Cycle tourists who ride 'moving on' tours, or trans-continental treks, don't encounter this problem. Because their Routes are always classical one-place-to-another, or 'linear' Routes, and it is just the natural order of things that the 'next' point will always be closer than any later points, so everything works just fine.
(Even a C-shaped route that covers a lot of ground but finishes only a short distance away, is usually perfectly OK as long as the first few Routepoints take you away from the final destination.)
For day-riders, well, once you understand what is going on then of course it's possible to place your Routepoints carefully, especially the first few (which should be close together) and the final one (which should be well away from the first 2 or 3). Even so, some route configurations do pose difficulties - for example, a figure-of-eight route, or a circular route where the first and last sections are out-and-back along the same roads.
Even these difficult routes can be programmed, but there is a much more simple solution to the problem. Simply split the Route into two (or more, but usually just two will do the trick). Essentially you break your ride down into 'out' and 'back' Routes, and just swap from one to the other during the lunch stop, say. You convert your circular route, or whatever configuration it is, into 2 (or more) linear Routes. Fortunately most Garmins can store large numbers of Routes (50 is common) so splitting into two doesn't pose any storage problems - and switching Routes only takes a few seconds.
Software such as Mapsource, and the many online planning aids such as BikeHike, don't offer an option to 'split' a Route. In Mapsource, the simple procedure is to 'duplicate' your Route - in other software you can do something similar using a 'save as' procedure. Make sure to name the two copies in such a way that you will be able to see which is which in the Garmin menu - eg call them 'A-Wobbly200' and 'B-Wobbly200'. Now open the 'properties' of your Route A and delete the last several points (eg, if the Route has 100 points, delete the last 30 say). That's it - you don't need to edit Route B at all. On the day, set off following Route A and at some convenient time during the day, just switch to Route B.
Some basic stuff:
Living with a Garmin: Etrex Basic Setup
Definition of Terms eg Route, Track etc
Living with a Garmin: Battery Runtime and Etrex Jitter
Living with a Garmin: The Waypoints Limitation
Living with a Garmin: The Follow Road Trap
Living with a Garmin: The Circular Routes Problem
Living with a Garmin: Declutter the Page Sequence
Living with a Garmin: Living with Mapsource Maps
Living with a Garmin: Waypoint Naming (for direct-style routes)
Living with a Garmin: Colour your Tracks and Routes
Living with a Garmin: Create a Route on the GPS
Top 5 GPS Tips (pdf) reprint of Arrivee article published Feb 2007
Some GPS FAQs web version of Arrivee article published Nov 2008
NEW - Garmin Etrex 20/30 essays:
Etrex 30 review reprint of Arrivee article published Jan 2012
Etrex 20 & 30, Basic Setup
Taming the Etrex 20/30: Restore the 'Page' key.
Dakota 20 review reprint of Arrivee article published Feb 2010
Living with a Garmin: Waypoint Naming and the Dakota 20 / Etrex 30
More Garmin essays - not-so-basic:
Garmin Etrex C Menu Map (pdf, July 2008)
Living with a Garmin: Full Reset
Living with a Garmin: Track, Route or Autoroute
Living with a Garmin: Three Ways to Beat the Waypoint Limit
Living with a Garmin: Three Ways to Beat the Trackpoint Limit
Living with a Garmin: Less is More
Living with a Garmin: Add Contours to your GPS Maps
Living with a Garmin: Struggling with GPX &... More GPX
Living with a Garmin: Screens you don't see every day
Living with a Garmin: Downgrade your Mapsource
Living with a Garmin: Put an OSM Map on your Garmin
Living with a Garmin: GPS Soak Test files to test your GPS waypoint capacity
OpenStreetMap and Mapsource Add OSM to your Mapsource collection
A Google Maps Workflow Create, Edit, Save, Share and Export a route