Sat Nav is short for Satelite Navigation and is normally associated with car trips in this type of app, for example most hotels, pubs etc offer "directions" which one then "sends to their mobile phone", which then guides the user visually and/or audibly to their "destination".
We hasten to remark however that while such features CAN be replicated (with varying degrees of accuracy) for walks such as the South Downs Way, safety? concerns presently seem to be influencing the format of the so called "Beta" offerings from Google as discussed below. In any case once "on the trail" the conventional trail markers should always be relied upon with sat nav being used as a "helper". Furthermore we are hoping that you will always have your mobile "tuned in" to facilitate finding that "perfect pano" to plonk into this app.
But we are just as quick to dispense with the great deal of pedantry surrounding sat nav that is simply an excuse for ignorance and laziness, for indeed the use of sat nav extends beyond the conventional "turn by turn" instructions and two words that come to mind to debunk most of these bleats (kinda like a Tweet from a sheep) are "backup battery" and "offline maps", and don't forget to "cache" your walk while still in wi-fi areas. Also the flyovers can assist with navigation in "seeing the wood from the trees" so consider saving the flyover for that walk, at least on a temporary basis. In fact the iphone format allows you to divide up the video into instant "bite size" sections of 15 seconds which allows you to view about a quarter of a mile before walking it, and then the same for the next section.
But the Google word one needs to understand is "DRAGS" (nothing to do with our nice gay friends) and the following map explains all.
This is the Walk 9 which we have fully populated with 11 panorama entry points and the orange line has been laboriously cloned from the "Domesday Map" at the National Trails site (trade secret but we have made the file public). Then the blue line (the ticked one) is the eastbound sat nav direction track which started as the two end points and was then dragged at many points along the way to make it "behave" and follow the orange line. For most Walks that was fully possible but as you can see here there is one path where a false one-way tag has upset the applecart as shown on the left below.
Then on the right, if you tick the westbound walk you see that the former problem has disappeared but a new problem exists slightly north. Google give a provision for reporting such issues and we have done so, meaning that it should be fixed shortly if the Google-God sees fit.
But a greater issue exists which hopefully is only temporary given that the blue lines above are in the Beta stage and smelling like they are heading in the right direction. The issue is that if you goto any of the tabs for sat nav like this on a desktop style computer (ie non mobile) you will get the full DRAGGED route we have laboriously formulated to follow the South Downs Way and be able to use the PREVIEW facility to do a full "turn by turn" trip complete with panoramas (if they are there that is).
However the same attempt on a mobile device gives the warning "Dragging does not affect sent route" and sure enough simply gives the normal shortest routes as if to say we wasted our time.
So rather than taking the pedantry path of saying "sat nav don't work so we are staying with the medieval Domesday maps" we provide all that DOES work with the intention of updating once Google has things sorted out fully, as the Google-Gods always do. But if you have any better understanding of these matters please let us know.
Later investigations say a Google forum on this matter was started maybe 2009 and closed in 2014 so fat chance of this getting fixed normally, but we are talking here to a nation that says "and we will NEVER give in" so let's fire up the steam driven computer at Bletchley Park and bingo we find "a STOP (aka Destination) is as good as a DRAG to a blind sheep" meaning that mobile devices DO obey a route created using destinations rather than drags.
Unfortunately it is even more laborious to create and a bit clunky to use where a stop is created in the middle of nowhere to bend a path and the mobile device says "you have arrived" and there is nothing there but a sheep (blind or not!). Anyway that is what we are "beta-ing" at present, subject to more road testing. Also there is a limit of only 10 destinations to play with for each route.
There is always the chance that the "Tracking Map" in Frame 3 of the Digital Track Card may spring to life at any time sat nav wise.
But as great as these Google offerings may be, Google only exists because of advertising revenue and this surely is the "conflict of interest" with the National Trails site that caused this roadblock where the words "For example, local businesses can highlight places to stay or eat on the maps" are relevant to the discussion.
In fact local businesses are provisionally listed BY Google with an invitation to "Claim this business" whereby commissions on bookings generates the income stream for Google. But unless our memories deceive us the same applied to the listings on the National Trails maps whereby a fee was charged for a "full" listing of a business.
As we now look in 2018 all is totally free at the National Trails maps so to use that lovely legal term "minds were turned" to this issue. Now any "mortal" who has actually applied for a Trekker loan will know it is NOT done by a phone call but by a fairly complex form that settles all these possible conflicts BEFORE one gets their hands on the Trekker (or in fact even a reply), so it looks like Google was overly quick to "get the contract" for all the National Trails in one fell swoop.
But who really cares as "the winner is the WALKER" as she/he now has access to both the National Trails listings and the Google listings, so is most unlikely to need to spend a night "under the stars".
Finally we endorse the words of Ben Bessant above and would add more. The question might arise as to WHY we would go to the trouble of the 23 steps outlined above of creating an app such as this (or in fact a whole series of such apps, mostly in England).
The answer is not logical as it involves a host of intangible matters which can be grouped under the expression "a labour of love", where even though I can tick the boxes of "older people" and "impaired mobility" (with "wealth deficiency" and "tyranny of distance" thrown in) there lingers that glimmer of hope that I may just be able to see some of these places first hand before taking the Big Walk. But if not, finding and mapping a selection of these brilliant panoramas (by Google or private folk) is a very good substitute and makes all the hard slog aspects worth the effort.
However at the top of my bucket list before that time would be to return once again to "England's green and pleasant land" and take the final plonk-a-pano to complete this app.