## Thursday, April 17, 2008

### Exactly how long is the Heysen Trail?

Estimates vary as to exactly how long the Heysen Trail actually is, although it is generally accepted that the trail is approximately 1,200km long. Is this really a good assumption to make though in calculating my percentage done and remaining?

This blog entry is tediously boring if you don't care how long the trail is. Really, what is the difference between whether it is 1,110km long or 1,200km long? Whichever it is, I and many others will walk the entire thing regardless. Don't say I didn't warn you... (although there is a short story about how someone walked 208 miles all the while measuring the distance with a short chain).

I've been keeping a tally of how much of the trail I have walked thus far - 740km, and have been regularly comparing this to the total trail length to see how much of a percentage I have achieved, and how much of a percentage I have left. I've accepted it as 1,200km, however now as I near the end, I don't want to have 10% still remaining on my last walk, only to discover 20km later at the trail head that the trail is shorter than 1,200km, or indeed longer!

Some sources claim the trail is 1,500km long - noted though only a few sources, few of which can be considered reliable. Some state this as the total distance including hills, ie the total steps taken - but this is simply not how you measure distances. Distances are measured from point A to point B via the given path assuming the land is dead flat.

The official guidebooks (published by the government Department for Environment and Heritage) give the distance each chapter covers, and this figure totals between 1,074km and 1,089km. Quite a bit smaller than the 1,200km they claim elsewhere in the introductions to the two guidebooks. However, I noted that some chapter estimates seem too low, particularly the last few chapters of the second guidebook.

There are spur trails and alternate routes along some sections of the trail and some people have used this to explain the disparity in the trail lengths.

John Chapman (www.john.chapman.name/sa-heys.html) seems to have devoted quite some time to determining how long the trail is, deciding the trail is 1,144km long. He refers to two articles that appeared in the Friends of the Heysen Trail magazine and the Adelaide Bushwalkers' magazine that stated the trail to be 1,060km long (the claim isn't referenced with magazine issues/dates). He arrived at 1,144km by using two potentially reliable sources for 2/3 of the trail, and measuring the remaining 1/3 using maps. Assuming the two sources are reliable, the method for the remaining 1/3 will not have been as accurate. However, it does seem to indicate that the 1,200km figure is inflated.

I do have access to a GPS survey, apparently undertaken in 2000 by some university students surveying the entire trail. This file, infinitely more accurate than other sources, measures the trail as 1,175km in length, including spur trails and alternate routes. Using this data, the spur trails and alternate routes total 65km, so depending on which of the alternate routes you use (I favoured the ones I walked) this gives the total trail length as 1,110km. It should be noted though, that there have been numerous re-routes of the trail since 2000, although I would largely expect that in the give and take they would more or less equal out.

It seems very reasonable to me to use this 1,110km figure as the length. I had one further check to make to confirm it's reliability. I had determined that to date (23 April 2008), I had walked 740km of the trail. The figures used to calculate this come from my own GPS unit distances from each walk, and before August 2007, other people's GPS unit distances. With other people's GPS distances, I've tried to keep this as true as possible by rounding both down and up (within 0.5km) to try and keep an accurate overall figure.

Using the GPS survey, I calculated the length of my remaining walks - which amounted to 369km. Hesitantly, I did some sums: 1,110km minus 369km would equal the amount already walked, which in this sum was 741km - just 1 kilometre off my accumulated total of what I have walked. I was quite pleased that the sums added up so well - at first glance this double-check confirms the 1,110km length from the GPS survey. It does use 33% of that same GPS survey (ie the bit of the trail not yet walked) in the proof sums so probably can't be used as definitive proof, but I hope that as I walk the estimated remaining 369km, my own GPS unit will confirm this figure - hopefully to be 1,110km, plus or minus 1%? Which would be 1,099km to 1,121km. I'll report back in August this year my findings (if I still care). Of course, as already noted, re-routes might affect the overall trail length within a small percentage.

In the meantime though, and without going to the length Richard Norwood went to in 1633 to determine the size of the earth (he spent two years walking the 208 miles between London and York, all the while measuring with a short length of chain), I can use 1,110km figure to calculate my trail percentages, and hopefully not have to make any adjustments to that percentage as I near the end of the trail. I'm quite looking forward to getting into the nineties percentage points! So to date, I have completed 66% of the trail.

Note: the original GPS survey file is 17MB, so I can't offer it up here for cross-examination. It has however formed the basis of the KML file used in the Google Maps on the Friends of the Heysen Trail website.