Monday, 14 April 2014

10 years of footpath mapping for OpenStreetMap

On a Saturday in late March I joined Nick Whitlegg, one of the earliest OpenStreetMap contributors, for a session mapping footpaths in the Weald. I was introduced to Nick several years ago on the basis that we were both walkers. But this was the first time we'd actually done a walk together, and my first opportunity to see how a real expert on footpath mapping did things.

Nickw with lots of footpath detail needing mapping
near Ockley, Surrey

Nick is a classic example of someone who had already started trying to combine technology, maps and leisure interests before they came to OpenStreetMap. It has often struck me talking to OSM contributors who loosely fall into the same demographic as me is the degree to which many of them were already actively doing this kind of thing, but hadn't found the right technology mix until they found OSM.

I certainly did: my first attempts at using maps for visualisations were done with MacDraw, later on I used CorelDraw (partly because it came with some good map files), and then Visio. I was still playing with Visio as late as 2003. When I got involved with volunteering at nature reserves my interest in mapping things was re-awakened and I made some use of a GIS product called MapMaker Gratis (not to be confused with Google MapMaker), and even played around with trying to warp old maps with this software. So although I was not an early adopter of OSM, only starting in late 2008, I knew all the things which had frustrated my earlier attempts. This meant that once I started using it, I very quickly could see that it had addressed most of these problems quite effectively.

Off the top of my head I can think of a number of British OSM contributors (Richard Fairhurst, Mike Collinson, SomeoneElse and Nick Whitlegg) who all had been collecting map data and creating or trying to create map applications before getting active in OSM, A good example is Richard's New Adelstrop Railway Atlas (I have a sneaky feeling that involvement in OSM was one of the reasons this was not completed). I'm sure each of their specific needs were different, some wanter maps for personal use others for business: but, like me, each recognised that what Steve Coast created provided a sound basis to build on.

Half way round our walk Nick remarked that he collected the first data for his Freemap project on 21st March 2004, 10 years and 1 day earlier. As soon as he was aware of OSM, Nick moved his data there and has been mapping footpaths in Europe and North America ever since. Thus we were also celebrating 10 years of data collection for OSM slightly before the official birthday in August.

Footpaths in the Weald and West Sussex

Our starting point was Ockley station (one my late 1970s maps I had with me that day called it Ockley and Capel Station). We'd chosen this on the basis of gaps in the coverage of public rights of way in Surrey and Sussex. Nick already knew there were significant gaps S of Cranleigh: at least in part because the area is not particularly accessible by public transport.

Years ago I did a fair bit of walking in the area: when I was first in London as a postgraduate student I was fairly desperate to get out of the city and tended to head South by train. I can recall three biggish walks in this area in the past: a tedious slog along an old railway line on a hot day (the Downs Link), and two rather pleasanter walks which led to pubs in Ewhurst and Rudgwick for lunch. So although I can no longer remember the precise details of the routes, refreshing my memory of the area is likely to prompt more recall.

As a complete aside, one of the odder places I've walked in South-East England is around Thorney Island, which is a military base. Access to the footpath is a little unusual, as shown below.

Amazingly this is a public right of way!
Thorney Island
Like most parts of Southern England, this area has plenty of rights of way: so common that it's often feasible to create a perfectly good circular walk which avoids roads even without a detailed map.n Paths are also regularly used, unlike in Carmarthenshire.

In general our search for paths used the council shapefiles from rowmaps. Both Nick and I had created overlays showing routes which appear to be missing on OSM. Nick's was more useful because it was on his smartphone as part of his Opentrail app (definitely a believer in eating his own dog food). Even if we walked a path we also had to see at least one guidepost or waymarker indicating the status of the path. In this part of the country it is very easy to follow another path and think one is still on a PRoW (Public Right of Way) (right at the end of the day we came across a path which seems to have been marked as a PRoW in error).

A couple of days before going out I'd prepared a first draft of my map of missing Surrey footpaths and discovered (as I knew I would at some stage) that an OSM mapper in the area has red-green colour-blindness. I had to fairly quickly experiment with changing my base visualisation with a little help from Coblis, more about this another time).

Missing footpaths in the Capel/Ockley area (highlighted in Blue)
Sources: OSM contributors, Ordnance Survey Open Data Meridian Crown copyright and database right OSGB, Surrey PRoW (Surrey County Council via rowmaps)


Although the station is now called Ockley it is much closer to Capel. I had about 45 minutes before Nick was due to arrive, so I pottered around in the Capel direction because I knew our target was Ockley. I was able to add a little detail around the station, and note a closed footpath just beyond the railway bridge. I then walked down to the main road and found the start of a footpath on the other side. Although I found a stile with an arrow painted on it suggesting the route for the next bit of the path, it did not look very promising, particularly as there was an electric fence inside the wooden fence.

Does the footpath really go this way?
Capel, Surrey

When Nick arrived we couldn't use the original path planned (it was closed because of a landslip on the railway embankment caused by recent wet weather), but very quickly found an adequate substitute about 400 metres further along. This took us along the edge of a field which didn't seem to be farmed and then into pleasant woodland. Many fields in the Weald are surrounded by fairly narrow wood belts, but many of these appeared to be original woodland (typically with carpets of bluebell leaves) rather than plantations. By British standards this is heavily wooded countryside.

Hazel Coppice beside the path

Another aspect of this countryside which we came across again and again through the day was that streams were deeply incised into the surrounding landscape (see main photo). These narrow valleys, which Nick believes are locally known as "Gullys" are nearly always wooded. Typically they were about 10 m below the prevailing land surface but sometimes more. In many ways they are reminiscent of places on the Mercia Mudstones above the Trent valley which are known as "dumbles". The geomorphology is probably quite different, as the Dumbles are a peri-glacial phenomenon associated with the lower sea levels of the time and the large water flows from melting glaciers , which caused deep cutting  into quite weak strata.

Beyond our first stream we came to a nexus of paths on the outskirts of Ockley. These took some interpreting (and I'm not sure we captured all of them) because of lost field boundaries. At one point we found an isolated stile still retaining footpath waymarkers. A direct line across a ploughed field took us out at the North end of Ockley next to the Village Hall.

Ockley is set either side of an old Roman Road (to Chichester) and has a long wide village green. I'd forgotten what an attractive setting it has. We didn't pause, but crossed the green to our next path. Later on checking my photos I discovered that one of the roads out of Ockley had been misnamed. Intrguingly the incorrect name (Lake Road) is present on both Ordnance Survey Open Data and Google Maps (despite the StreetView cameras having obviously photographed the name on the sign).


From Ockley our target was a small hamlet called Walliswood: notably because it had a pub which we seemed likely to reach at the right time for a lunch break. The Weald is full of small dispersed hamlets like this one: these days often with discrete big houses set back and the gardens almost enclosed by woods. An excellent network of paths led us to within 100m of the door of the Scarlett Arms, with a mix of fields, woods and a golf course.

Scarlett Arms by Mark Percy on Geograph
 © Copyright Mark Percy and licensed for reuse under this Creative Commons Licence.

We also came across a small patch of "Unimproved Grassland" managed by the Surrey Wildlife Trust: for once a real meadow.

Unimproved Grassland interpretation panel

The pub was pleasantly unpretentious, with a smouldering fire and decent beer. I've found in the past that after a pub lunch walking isn't as enjoyable as it could be, so I was happy to agree to Nick's suggestion of not eating in the pub. I had sandwiches anyway. When we did start again I felt fresher than if I'd eaten.

Getting Serious

After lunch we continued, first heading SW and then working northwards with a view to returning to the S end of Ockley and then back to the station by a completely different route. The countryside we passed through was again similar to that we had already seen, but the sun shone and we had good views of Leith Hill to the N.

Some time near 15:30 Nick really got into his stride, and we started doing circular loops to capture more footpaths. After the first of these I realised I was not going to keep up his pace, so we split with Nick taking the longer side of a loop whilst I walked the shorter one. One of mine took me back across the golf course, and required a fair bit of sleuthing to find the footpath guideposts and from there reconstruct the actual route of the path.

View of Leith Hill from near Forest Green

By the time we got to Ockley I was slowing down to the extent that I knew I had to properly pace myself to ensure we got back in adequate time for the last train at 18:36. A really steep descent into and climb out of the nature reserve at slowed me up more, but thereafter the return was largely along metalled roads and I once again found a decent sustainable pace.

I suspect that Nick didn't map quite as much as he would have done on his own, but nonetheless I think we achieved a decent bit of mapping, adding something like 20 km of paths which had not been mapped, and improving information on several others. In many ways mapping was subsidiary in that we had a long walk through attractive countryside on a nice spring day, which was reward enough in itself.

A repeat

In fact we both enjoyed it enough to repeat the exercise last Saturday (11th April) in West Sussex between Midhurst and Petworth. We adopted a similar format, but did more mapping before stopping for a break at a pub. To my fascination the pub had geological maps of the local area at the bar. An innovation which I very much enjoyed.

Footpath mapping around Midhurst, April 2014
Mapping footpaths for OpenStreetMap April 2014
Route is shown as a pale line over the Thunderforest Landscape layer
Potentially missing PRoWs are shown in blue (from West Sussex council via rowmaps)
 This time I had my proper camera with me, and took many many photos. Just a couple from the end of the day might give some feel for the places:

Lovely evening light, Tillington
Evening light on new leaves, Tillington

Above Tillington at Pitshill, I found that some pre-existing paths had been moved. These turn out to be the paths involved in a well-known legal battle between the landowner and the Ramblers Association, which the landowner won. I was able to get GPS traces for the upper-half of the new alignment and remove paths which now don't exist. So even in the countryside, it's important to continually verify OSM mapping. Also in this area many paths are poorly aligned and could do with double checking.
Evening vista of South Downs
Vineyard on the Greensand Ridge looking SW to the South Downs

This was countryside I'd never visited before, and it's a bit different from the other parts of the Weald. In the past when travelling this far I'd always gone to the next ridge of hills, the South Downs (now a National Park), and, unjustly, ignored the Greensand Ridge.

Needless to say we already have a provisional date for our next joint expedition.

1 comment:

  1. Hi!
    Great post -- adding walking & cycling data are big reasons why I too joined OSM (as well as being a general map geek). Just wanted to ask a couple of questions re Surrey's fantastic PROW data:
    (a) If I survey the existence of a path without PROW signposting (that I can see), but it's shown as a PROW on the Surrey map, is it appropriate to add "designation=xxx" to the way in OSM?
    (b) Similarly, is it appropriate to add PROW ref nos. from the Surrey dataset to ways in OSM (using the "prow_ref=xxx" tag) if they are not shown on signposts?
    David (OSM user Pgd81, in Croydon, not-quite-Surrey)